Support last event Id for resumability of sse

[bperhaps]

Implemented SSE resumability/redelivery support for Streamable HTTP by introducing an event-store abstraction, adding in-memory event persistence/replay, wiring Last-Event-ID handling through server session/transport layers, and adding comprehensive unit/integration tests.

I haven't discussed this PR enough, so I haven't created enough Java doc documentation and tests. If there's a chance this PR will be merged, I'll try to improve it.

Motivation and Context

Implementation of MCP documentation.

How Has This Been Tested?

I worte some tests, and also i play it on my device.

Breaking Changes

nop

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

[Kehrlann]

Resumability is abandoned in the upcoming 2026-07-28 spec, see spec > transport > streamable > earlier revisions. We don't want to invest in resumability support if it's bound to go away ; our session storage wouldn't allow it at scale anyway.