fix: compilation with --no-default-features

[Vaiz]

Motivation and Context

This is a pretty simple change that fixes feature gates in a couple of places. It allows to use rmcp crate in server mode without enabling macros and base64 features reducing the dependency tree for applications that don't use those capabilities.

How Has This Been Tested?

I verified that it actually compiles now
cargo build -p rmcp --no-default-features --features server

Breaking Changes

There are no breaking changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)

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

[alexhancock]

@Vaiz LGTM. If you can adjust the commit message to follow https://www.conventionalcommits.org/en/v1.0.0/ we can merge

I am also going to add a pre-commit hook for this.

[Vaiz]

@Vaiz LGTM. If you can adjust the commit message to follow https://www.conventionalcommits.org/en/v1.0.0/ we can merge

I am also going to add a pre-commit hook for this.

@alexhancock , thanks for looking into that.
I've adjusted commit message, should be fine now