feat: remove checked-in Rust binaries (#286)

All users must currently build the tools from sources with rules_rust.

As a separate PR I will introduce a new toolchain that uses our typical
repository rule constructs from bazel-lib to fetch the pre-built release
binaries.

---

### Type of change

- Refactor (a code change that neither fixes a bug or adds a new
feature)

**For changes visible to end-users**

- Breaking change (this change will force users to change their own code
or config)

Users must now register a rust toolchain, or else wait for the next
release of rules_py.

### Test plan

- Covered by existing test cases

e2e/smoke covers this, though it sadly needs a bunch of additions.

Author: alexeagle

.bcr/patches/rust_dev_dep.patch

@@ -0,0 +1,36 @@
+diff --git a/MODULE.bazel b/MODULE.bazel
+index 842544e..5e5ee92 100644
+--- a/MODULE.bazel
++++ b/MODULE.bazel
+@@ -32,13 +32,13 @@ register_toolchains(
+ bazel_dep(
+     name = "rules_rust",
+     version = "0.38.0",
+-    # In released versions: dev_dependency = True
++    dev_dependency = True
+ )
+ 
+ rust = use_extension(
+     "@rules_rust//rust:extensions.bzl",
+     "rust",
+-    # In released versions: dev_dependency = True
++    dev_dependency = True
+ )
+ 
+ rust.toolchain(
+@@ -49,13 +49,13 @@ use_repo(rust, "rust_toolchains")
+ 
+ register_toolchains(
+     "@rust_toolchains//:all",
+-    # In released versions: dev_dependency = True
++    dev_dependency = True
+ )
+ 
+ crate = use_extension(
+     "@rules_rust//crate_universe:extension.bzl",
+     "crate",
+-    # In released versions: dev_dependency = True
++    dev_dependency = True
+ )
+ 
+ crate.from_cargo(

MODULE.bazel

@@ -24,3 +24,51 @@ register_toolchains(
     "@aspect_rules_py//py/private/toolchain/venv/...",
     "@aspect_rules_py//py/private/toolchain/unpack/...",
 )
+
+# To allow Rust binaries in /py/tools to be built from source
+# NOTE: when publishing to BCR, we patch these to be dev_dependency, as we publish pre-built binaries
+# along with our releases.
+
+bazel_dep(
+    name = "rules_rust",
+    version = "0.38.0",
+    # In released versions: dev_dependency = True
+)
+
+rust = use_extension(
+    "@rules_rust//rust:extensions.bzl",
+    "rust",
+    # In released versions: dev_dependency = True
+)
+
+rust.toolchain(
+    edition = "2021",
+    versions = ["1.74.1"],
+)
+use_repo(rust, "rust_toolchains")
+
+register_toolchains(
+    "@rust_toolchains//:all",
+    # In released versions: dev_dependency = True
+)
+
+crate = use_extension(
+    "@rules_rust//crate_universe:extension.bzl",
+    "crate",
+    # In released versions: dev_dependency = True
+)
+
+crate.from_cargo(
+    name = "crate_index",
+    cargo_lockfile = "//:Cargo.lock",
+    # Apparently not needed under bzlmod?
+    # lockfile = "//:Cargo.Bazel.lock",
+    manifests = [
+        "//:Cargo.toml",
+        "//py/tools/py:Cargo.toml",
+        "//py/tools/venv_bin:Cargo.toml",
+        "//py/tools/unpack_bin:Cargo.toml",
+    ],
+)
+
+use_repo(crate, "crate_index")