fix(mcp): upgrade rmcp dependency from 1.x to 3.4

[StefanSteiner]

Summary

• Upgrades hyperdb-mcp's rmcp MCP SDK dependency from 1.x (1.8.0) to 3.4.0, resolving the outstanding rmcp Dependabot security advisories.
• hyperdb-mcp is stdio-only (no SSE/HTTP transport used anywhere in this repo), so the actual runtime exposure from these CVEs was already near-zero — this migration closes the alerts and picks up the newer SDK's capabilities.
• No change to the MCP wire protocol or tool surface this server exposes; hyperdb-mcp/CHANGELOG.md records it as an internal dependency bump.

API surface migrated

• Content → ContentBlock
• RawResource / RawResourceTemplate → Resource / ResourceTemplate (builder pattern; the AnnotateAble trait and .no_annotation() are gone — annotations default to None)
• PromptMessageRole → Role
• ServerInfo / ClientInfo → ServerConfig / ClientConfig (deprecated aliases, same underlying type)
• ListResourcesResult / ListResourceTemplatesResult now built via ::with_all_items(items) (new SEP-2549 cache-hint fields)
• read_resource now returns ReadResourceResponse (new SEP-2549/MRTR wrapper around ReadResourceResult)
• ResourceUpdatedNotificationParam is #[non_exhaustive], constructed via ::new(uri)
• Two test call sites intentionally keep exercising the deprecated resources/subscribe client method (the server still implements that legacy protocol path via SubscriptionRegistry), suppressed with a reasoned #[allow(deprecated)]

Test plan

• cargo check --workspace --all-targets — clean, 0 errors
• cargo test -p hyperdb-mcp --all-targets against the pinned .hyperd/current engine — all targets pass, 0 failures
• cargo clippy --workspace --all-targets --all-features -- -D warnings (CI's exact command) — clean, 0 warnings
• cargo fmt --all — no diff
• cargo audit — 0 vulnerabilities (rmcp advisories no longer present)
• cargo deny check advisories — advisories ok
• npx markdownlint-cli2 on the touched CHANGELOG.md — 0 issues