Set minimal supported Rust version to 1.82.0 (#572)

According to cargo-msrv:

```
❯ cargo msrv find --linear
...

  │ 2723 | unsafe extern "C" {                                                                                                                 │
  │      | ^^^^^^                                                                                                                              │
  │      |                                                                                                                                     │
  │      = note: see issue #123743 <rust-lang/rust#123743> for more information                                      │
  │                                                                                                                                            │
  │ error: extern block cannot be declared unsafe                                                                                              │
  │     --> /Users/mathias/devel/duckdb/duckdb-rs/target/aarch64-apple-darwin/debug/build/libduckdb-sys-effbdf83ad7002d1/out/bindgen.rs:2732:1 │
  │      |                                                                                                                                     │
  │ 2732 | unsafe extern "C" {                                                                                                                 │
  │      | ^^^^^^                                                                                                                              │
  │      |                                                                                                                                     │
  │      = note: see issue #123743 <rust-lang/rust#123743> for more information                                      │
  │                                                                                                                                            │
  │ error: extern block cannot be declared unsafe                                                                                              │
  │     --> /Users/mathias/devel/duckdb/duckdb-rs/target/aarch64-apple-darwin/debug/build/libduckdb-sys-effbdf83ad7002d1/out/bindgen.rs:2736:1 │
  │      |                                                                                                                                     │
  │ 2736 | unsafe extern "C" {                                                                                                                 │
  │      | ^^^^^^                                                                                                                              │
  │      |                                                                                                                                     │
  │      = note: see issue #123743 <rust-lang/rust#123743> for more information                                      │
  │                                                                                                                                            │
  │ error: could not compile `libduckdb-sys` (lib) due to 428 previous errors                                                                  │
  │                                                                                                                                            │
  ╰────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯


Result:
   Considered (min … max):   Rust 0.11.0 … Rust 1.88.0
   Search method:            linear
   MSRV:                     1.82.0
   Target:                   aarch64-apple-darwin
```

Arrow 55 also requires at least Rust 1.81:

```
❯ cargo b
error: package `arrow-ord v55.2.0` cannot be built because it requires rustc 1.81 or newer, while the currently active rustc version is 1.70.0
Either upgrade to rustc 1.81 or newer, or use
cargo update -p [email protected] --precise ver
where `ver` is the latest version of `arrow-ord` supporting rustc 1.70.0
```

Rust 1.82 was released almost a year ago in October 2024, so it's not
too demanding on users.

Note that I didn't touch the Rust edition because Rust 2024 was only
stable in Rust 1.85.

Besides adding the Rust version to Cargo.toml, I also added a version
policy to our README (inspired by
[arrow-rs](https://github.com/apache/arrow-rs?tab=readme-ov-file#rust-version-compatibility-policy)).

Fixes #570

Author: mlafeldt

Cargo.toml

@@ -9,14 +9,15 @@ members = [
 [workspace.package]
 version = "1.3.2"
 authors = ["wangfenjin <[email protected]>"]
-edition = "2021"
 repository = "https://github.com/duckdb/duckdb-rs"
 homepage = "https://github.com/duckdb/duckdb-rs"
 documentation = "http://docs.rs/duckdb/"
 readme = "README.md"
 keywords = ["duckdb", "database", "ffi"]
 license = "MIT"
 categories = ["database"]
+edition = "2021"
+rust-version = "1.82.0"
 
 [workspace.dependencies]
 duckdb = { version = "=1.3.2", path = "crates/duckdb" }

README.md

@@ -200,6 +200,10 @@ If you use the `bundled` features, you will get pregenerated bindings for the
 bundled version of DuckDB. If you want to run `bindgen` at buildtime to
 produce your own bindings, use the `buildtime_bindgen` Cargo feature.
 
+## Rust version compatibility
+
+duckdb-rs is built and tested with stable Rust, and will keep a rolling MSRV (minimum supported Rust version) that can only be updated in major and minor releases on a need by basis (e.g. project dependencies bump their MSRV or a particular Rust feature is useful for us etc.). The new MSRV will be at least 6 months old. Patch releases are guaranteed to have the same MSRV.
+
 ## Contributing
 
 We welcome contributions! Take a look at [CONTRIBUTING.md](CONTRIBUTING.md) for more information.

crates/duckdb-loadable-macros/Cargo.toml

@@ -2,14 +2,15 @@
 name = "duckdb-loadable-macros"
 version = "0.1.9"
 authors = { workspace = true }
-edition = { workspace = true }
 license = { workspace = true }
 repository = { workspace = true }
 homepage = { workspace = true }
 keywords = { workspace = true }
 readme = { workspace = true }
 categories = ["external-ffi-bindings", "database"]
 description = "Native bindings to the libduckdb library, C API; build loadable extensions"
+edition = { workspace = true }
+rust-version = { workspace = true }
 
 [dependencies]
 darling = "0.20.10"

crates/duckdb/Cargo.toml

@@ -2,7 +2,6 @@
 name = "duckdb"
 version = "1.3.2"
 authors = { workspace = true }
-edition = { workspace = true }
 repository = { workspace = true }
 homepage = { workspace = true }
 documentation = { workspace = true }
@@ -11,6 +10,8 @@ keywords = { workspace = true }
 license = { workspace = true }
 categories = { workspace = true }
 description = "Ergonomic wrapper for DuckDB"
+edition = { workspace = true }
+rust-version = { workspace = true }
 
 [lib]
 name = "duckdb"

crates/libduckdb-sys/Cargo.toml

@@ -2,7 +2,6 @@
 name = "libduckdb-sys"
 version = "1.3.2"
 authors = { workspace = true }
-edition = { workspace = true }
 license = { workspace = true }
 repository = { workspace = true }
 homepage = { workspace = true }
@@ -12,6 +11,8 @@ build = "build.rs"
 categories = ["external-ffi-bindings", "database"]
 description = "Native bindings to the libduckdb library, C API"
 exclude = ["duckdb-sources"]
+edition = { workspace = true }
+rust-version = { workspace = true }
 
 [features]
 default = ["vcpkg", "pkg-config"]