fix(server): validate low-level tool inputs

[uuzzrm]

Fixes #2628

Summary

• Remember each tool inputSchema advertised by a low-level tools/list response for the active connection.
• Validate tools/call arguments before dispatch and return an isError tool result when the arguments do not match the advertised schema.
• Keep the high-level McpServer Standard Schema parsing path unchanged, including schemas that intentionally coerce or transform values.
• Add regression coverage for invalid and valid calls, connection-scoped schema state, custom JSON Schema validators, and high-level coercion.
• Update the low-level server and schema validator documentation and example.

Verification

Passed:

• pnpm lint:all
• pnpm typecheck:all
• pnpm build:all
• pnpm --filter @modelcontextprotocol/server test (42 files, 473 tests)
• pnpm --filter @modelcontextprotocol/examples typecheck
• pnpm --filter @modelcontextprotocol/examples exec tsx guides/advanced/low-level-server.examples.ts

The repository-wide pnpm test:all run was blocked by two existing examples/shared tests because the local environment could not load the better-sqlite3 native binding. The server, client, core, and middleware test suites completed successfully.

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commit: dc24b03