Cargo.toml: Add "rust-version" field

This is a field that describes current MSRV of the crate.
In the future it will be used by Cargo during resolving to get
versions compatible with users toolchain. For that reason we should
provide it.

Author: Lorak-mmk

scylla-cql/Cargo.toml

@@ -2,6 +2,7 @@
 name = "scylla-cql"
 version = "0.3.0"
 edition = "2021"
+rust-version = "1.70"
 description = "CQL data types and primitives, for interacting with Scylla."
 repository = "https://github.com/scylladb/scylla-rust-driver"
 readme = "../README.md"

scylla-macros/Cargo.toml

@@ -2,6 +2,7 @@
 name = "scylla-macros"
 version = "0.6.0"
 edition = "2021"
+rust-version = "1.70"
 description = "proc macros for scylla async CQL driver"
 repository = "https://github.com/scylladb/scylla-rust-driver"
 readme = "../README.md"

scylla-proxy/Cargo.toml

@@ -2,6 +2,7 @@
 name = "scylla-proxy"
 version = "0.0.3"
 edition = "2021"
+rust-version = "1.70"
 description = "Proxy layer between Scylla driver and cluster that enables testing Scylla drivers' behaviour in unfavourable conditions"
 repository = "https://github.com/scylladb/scylla-rust-driver"
 readme = "../README.md"

scylla/Cargo.toml

@@ -2,6 +2,7 @@
 name = "scylla"
 version = "0.14.0"
 edition = "2021"
+rust-version = "1.70"
 description = "Async CQL driver for Rust, optimized for Scylla, fully compatible with Apache Cassandra™"
 repository = "https://github.com/scylladb/scylla-rust-driver"
 readme = "../README.md"