fix: use MSRV-aware dependency resolver

[DaleSeo]

Motivation and Context

uuid 1.27.0 came out on Oct 2 and requires Rust 1.89. We don't commit Cargo.lock, so every CI run resolves the newest versions. The MSRV job now picks uuid 1.27.0 and fails with rustc 1.88.0 is not supported (seen on #1248). main passed only because its last run finished before the release. The next run will hit the same failure.

The workspace uses edition 2024, where resolver 3 is the default. But resolver = "2" was set explicitly, which turned off MSRV-aware fallback. With resolver 3, Cargo picks the newest version that works with 1.88 instead. Resolver settings apply only inside this workspace, so downstream users of rmcp are not affected.

How Has This Been Tested?

cargo +1.88 check --all-targets --all-features

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed