Remove the "needs alternate schema" mechanism in MCPClient, moving the necessary schema massaging into GeminiLLMAdapter instead.

This does a couple of things:
- Makes the `MCPClient` LLM agnostic, setting us up for some upcoming improvements (like making it possible to use with `LLMSwitcher`)
- Makes `GeminiLLMAdapter` more robust, as the schema massaging that was previously only done in `MCPClient` is useful for all tools, not just for MCP-provided ones

CHANGELOG.md

@@ -68,6 +68,11 @@ reason")`.
 - `GeminiLiveLLMService` now properly supports context-provided system
   instruction and tools.
 
+### Removed
+
+- Removed `needs_mcp_alternate_schema()` from `LLMService`. The mechanism that
+  relied on it went away.
+
 ## [0.0.92] - 2025-10-31 🎃 "The Haunted Edition" 👻
 
 ### Added