fix(memory): report package version in server info

[kingrubic]

Summary

• read the memory server version from its package.json at runtime
• use that package version for MCP serverInfo instead of a hardcoded value
• add a regression test for the package metadata lookup

Fixes #4406.

Verification

• npm run build --workspace @modelcontextprotocol/server-memory
• npm test --workspace @modelcontextprotocol/server-memory

[kingrubic]

Closing this PR to keep the backlog tidy after more than 48 hours without maintainer feedback. Please feel free to reopen it if a maintainer finds it useful. Thank you.