Upgrade reqwest to 0.13.2

[DaleSeo]

Motivation and Context

reqwest 0.13 ships with rustls as the default TLS backend and renames several TLS features. This PR bumps the SDK from reqwest 0.12 to 0.13.2 across the main library and all examples.

oauth2 v5.0 depends on reqwest ^0.12 through its built-in reqwest feature, which would pull in a second, incompatible copy of reqwest. To avoid that, we disable oauth2's reqwest feature and provide our own OAuthReqwestClient wrapper that implements oauth2::AsyncHttpClient against reqwest 0.13.

How Has This Been Tested?

All existing tests pass.

Breaking Changes

The user-facing TLS feature names (reqwest, reqwest-native-tls, reqwest-tls-no-provider) are unchanged. Users who also depend on reqwest directly will need to bump to "0.13" in their Cargo.toml so that types unify, but no code changes are needed.

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