chore(rmcp): remove dependency on chrono default features

[chitao1234]

Disable chrono default features for non-wasm rmcp builds and enable only the features rmcp actually uses. This avoids pulling unnecessary local-timezone support such as iana-time-zone / iana-time-zone-haiku, which can introduce avoidable platform library dependencies on Haiku. Fixes #828.

Motivation and Context

Issue #828 reports that rmcp’s native chrono dependency leaves default features enabled, which pulls in local-timezone support that rmcp does not use. On Haiku, that can bring in iana-time-zone-haiku and libbe.so, contributing to downstream link failures when combined with vendored zstd.

This change narrows the native chrono dependency to default-features = false with only ["serde", "now"] enabled. That keeps the functionalities rmcp uses while avoiding the extra dependency footprint from chrono defaults.

How Has This Been Tested?

cargo test -p rmcp, cargo test -p rmcp --all-features and cargo test --workspace --all under Linux x86_64

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

Additional context

See #828.