Add ToolAnnotations (readOnlyHint, etc.) to MCP tools

[nowsprinting]

Summary

Add MCP ToolAnnotations to each tool in this plugin to help clients (e.g., Claude Code)
understand whether a tool modifies state, so they can make better decisions about
auto-approval or confirmation prompts.

Planned Annotations per Tool

Tool	readOnlyHint	destructiveHint	idempotentHint	openWorldHint
get_unity_compilation_result	true	—	—	false
run_unity_tests	true	—	—	false
run_method_in_unity	false	true	false	false
unity_play_control	false	false	false	false

Notes:

• destructiveHint and idempotentHint are only set when readOnlyHint is false
• run_unity_tests: read-only because test execution does not persist state changes
• run_method_in_unity: destructiveHint is true — the called method is arbitrary

Prerequisite

This issue depends on JetBrains adding ToolAnnotations support to the McpToolset
extension point API.

Upstream feature request: https://youtrack.jetbrains.com/issue/IJPL-238125/MCP-Server-Support-ToolAnnotations-readOnlyHint-destructiveHint-etc.

Until IJPL-238125 is resolved and a new Rider release includes the fix, this issue
cannot be implemented.

References

• MCP specification — ToolAnnotations schema