Update MSRV to 1.70.0

[mooori]

Currently we still need to support Rust 1.69.0 for some users of this library. Once they are fine with upgrading to 1.70.0, we should bump near-plugin’s MSRV.

Reason: Using near-workspaces with Rust 1.69.0 requires manually downgrading some dependencies, which is bad developer experience and requires maintenance. (See the conversation in #118).

Tasks:

• Bump rust-version in ./Cargo.toml and channel in ./rust-toolchain
• Build test contracts with the new MSRV: bump channel in ./near-plugins-derive/tests/contracts/**/rust-toolchain
• Remove ./scripts/fix-dependencies.sh
  • Stop executing that script in CI