feat(plugin): align plugin tool types with built-in tool capabilities

[eXamadeus]

What does this PR do?

Fixes: #8327

Related: #8269, #8380

[!NOTE] This is complementary to the v2 SDK upgrade in #8380. This PR improves type safety of the ToolContext used for developing custom tools in plugins. The other PR is focused on upgrading the client capabilities for plugins. Similar, but slightly different goals.

This PR aligns plugin tool types with the capabilities tools already have. Specifically:

• Exposes ToolContext fields to plugin tools: callID, extra, ~metadata()~, and ~ask()~ to give plugins the correct context types
  • update: metadata() and ask() were added in #8269
• Adds ExecuteResult type allowing plugin tools to return structured result objects with title, metadata, output, and attachments instead of only plain strings
• Updates the registry to handle structured results from plugin tools, bypassing truncation when plugins return an ExecuteResult directly (assuming tools till truncate...we could add a check here?)
• Exports all useful intermediate-types so plugin authors can use them more ergonomically.

This enables plugins to provide richer tool responses with proper metadata updates, closer matching the flexibility of built-in tools.

How did you verify your code works?

• Added tests to ensure both string returns and object returns work as expected
• Ran TypeScript type checking
• Verified locally with a plugin in development that required proper metadata updates from plugin tools

The types all align nicely in the registry:

[!NOTE] Replaces #8328 because I needed to use the dev branch in my cloned repo for other things...GitHub wouldn't let me update the branch the PR originated from so I had to make a new one.