chore: refactor to remove global state

[pedroslopez]

What

When wiring up evals, we want to be able to run multiple "sessions" or connector builds within the same python process. The current structure makes this hard, since we use global variables to keep track of a few things, such as which directory we're writing to.

This PR refactors this "global state" that is relevant for a specific run of the agent into a SessionState that is passed around, in order to be able to call the method to run the agent multiple times within the same python process.

Note: most of this was done by Claude Code

How

• Introduce SessionState
• Move workspace_dir, execution_log_file, is_success, is_failed, start_time into the session state
• Rather than creating tools at a global level, which can have information such as which directory we're writing to in the case of the files tool, refactor into methods that create the tool, and uses it in the context of a particular session.
• Expose session_id as a parameter to the run_connector_build method. This is so we can explicitly pass a session ID to better control where things will be stored, allowing us to reference the workspace directory after the fact.

[github-actions]

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{
  "mcpServers": {
    "connector-builder-mcp-dev": {
      "command": "uvx",
      "args": ["--from", "git+https://github.com/airbytehq/connector-builder-mcp.git@pedro/no-globals", "connector-builder-mcp"]
    }
  }
}

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[github-actions]

PyTest Results (Fast)

0 tests  ±0   0 ✅ ±0   0s ⏱️ ±0s
0 suites ±0   0 💤 ±0 
0 files   ±0   0 ❌ ±0 

Results for commit 295aa4d. ± Comparison against base commit b03e56f.

♻️ This comment has been updated with latest results.

[aaronsteers]

LGTM!