feat(time): add tool annotations

[nielskaspers]

Summary

Adds MCP ToolAnnotations to both tools in the time server (get_current_time and convert_time), marking them as read-only, non-destructive, idempotent, and closed-world — matching the annotation coverage already present in server-filesystem.

Issue

Fixes #3574

Changes

• Import ToolAnnotations from mcp.types
• Add annotations parameter to both Tool() declarations with readOnlyHint=True, destructiveHint=False, idempotentHint=True, openWorldHint=False

Testing

• Metadata-only change; no behavioral impact
• Both tools are pure computations (system clock read and timezone conversion) with no side effects or external calls

[olaservo]

Both tool annotations are semantically correct:

• get_current_time: reads the system clock — pure read-only, closed-world.
• convert_time: timezone arithmetic using bundled zoneinfo data — pure computation, no external calls.

openWorldHint: false is correct for both (no network access). readOnlyHint: true is accurate.

Minor note: destructiveHint and idempotentHint are redundant when readOnlyHint is true per the MCP spec ("meaningful only when readOnlyHint == false"). The filesystem server omits them for its read-only tools. Not wrong to include them — just a style difference.

Also note: PR #3580 (fetch annotations) includes identical changes to this same time server file. If both merge, one will conflict. Recommend merging this PR first so #3580 can be scoped to fetch-only on rebase.

LGTM — thanks @nielskaspers!

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Reviewed with the assistance of Claude Code (claude-opus-4-6). Annotation semantics verified against the MCP specification and time server source code.