Add remove_prompt() and remove_resource() for parity with remove_tool()

[rgoldstein1989]

Description

MCPServer exposes remove_tool(name) (added in #1322) but has no equivalent for prompts or resources. This was part of the original ask in #711 ("removing a tool or resource dynamically"), which was closed when remove_tool() landed — but the resource and prompt sides were never addressed.

Use case

Multi-tenant / multi-instance deployments where the same server image serves different clients. Today users can filter tools per-instance via remove_tool(), but for prompts and resources they're forced to reach into private internals:

# Current workaround — fragile, undocumented
del mcp._prompt_manager._prompts["some_prompt"]
del mcp._resource_manager._resources[str(uri)]

(This is the same pattern @lukehsiao described in #711 (comment) for tools, before remove_tool() existed.)

Current state

Primitive	add_*	remove_*
Tool	add_tool() / @tool()	remove_tool() ✅
Prompt	add_prompt() / @prompt()	missing
Resource	add_resource() / @resource()	missing
Resource Template	add_template()	missing

Proposed API

Add these methods, mirroring the existing remove_tool() pattern exactly:

• PromptManager.remove_prompt(name: str) — raises PromptError if not found
• ResourceManager.remove_resource(uri: str) — raises ResourceError if not found
• ResourceManager.remove_template(uri_template: str) — raises ResourceError if not found
• MCPServer.remove_prompt(name) — thin wrapper delegating to the manager
• MCPServer.remove_resource(uri) — thin wrapper delegating to the manager
• MCPServer.remove_resource_template(uri_template) — thin wrapper delegating to the manager
• PromptError exception class in exceptions.py (for symmetry with ToolError and ResourceError)

This is ~15 lines of implementation across 4 source files, plus tests. Purely additive, no breaking changes.

References

• removing a tool or resource dynamically #711 — Original issue requesting dynamic tool/resource removal (closed, only tools were addressed)
• feat: add ability to remove tools #1322 — PR that added remove_tool() (the pattern this proposal follows)

[goingforstudying-ctrl]

Submitted PR #2333 to implement this: #2333

This adds remove_prompt(), remove_resource(), and remove_resource_template()
following the same pattern as remove_tool(). Please review when you have time. Thanks!

[rgoldstein1989]

Submitted PR #2335 as an alternative to #2333. It covers the same implementation scope but adds:

1. Tests — 11 tests mirroring the existing remove_tool patterns (remove existing, remove nonexistent, remove-and-list via client, remove-and-access via client) for all three primitives. Required to pass CI's 100% coverage gate.
2. AnyUrl | str type on remove_resource — normalizes with str(uri) before lookup, matching how get_resource() handles it.