Support removing tools

[tpaulshippy]

What this does

I realized recently just how many tokens tools can take.

Here's an example of saying "Hello" to Bedrock with 4 basic local tools + the tools from the Playwright MCP:

This call took 3024 input tokens.
Without the Playwright MCP, the call takes 842 tokens.

In a chat with an agentic interface, I want the option to add/remove tools at will to save on tokens.

It also simplifies tool selection for the LLM if there are fewer tools to choose from.

Type of change

• New feature

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
• I updated documentation if needed
• I didn't modify auto-generated files manually (models.json, aliases.json)

API changes

• New public methods/classes

Related issues

Resolves #229