Upgrade mypy to 2.1.0 and optimize type checking

[tsvikas]

Summary

This PR upgrades mypy from version 1.20.0 to 2.1.0 and optimizes the type checking configuration and CI workflow.

Key Changes

• Dependency upgrade: Updated mypy from ~=1.20.0 to ~=2.1.0 and removed the [native-parser] extra (no longer needed in 2.1.0)
• Configuration update: Removed local_partial_types = true from mypy config, which is no longer necessary with mypy 2.1.0
• Performance optimization: Added --num-workers 4 flag to mypy invocation in CI to parallelize type checking across 4 workers
• Documentation: Updated mypy version reference in config comments from 1.20 to 2.1

Implementation Details

The removal of local_partial_types configuration indicates that mypy 2.1.0 has improved its handling of partial types, making this explicit setting redundant. The parallel worker configuration in CI should reduce type checking time without requiring any code changes.

https://claude.ai/code/session_01DSZJX4JKn2or8vLdmoGECt

[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• Hard-coding --num-workers 4 in the CI workflow may underutilize or oversubscribe cores on different runners; consider either omitting the flag to use mypy’s default parallelism or deriving the worker count dynamically (e.g., via $(nproc) or a matrix/env variable).

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Hard-coding `--num-workers 4` in the CI workflow may underutilize or oversubscribe cores on different runners; consider either omitting the flag to use mypy’s default parallelism or deriving the worker count dynamically (e.g., via `$(nproc)` or a matrix/env variable).

## Individual Comments

### Comment 1
<location path="project_name/.github/workflows/ci.yml.jinja" line_range="79-80" />
<code_context>
         run: uv pip list
       - name: Run mypy
-        run: uv run --no-sync mypy
+        run: uv run --no-sync mypy --num-workers 4

   dependencies:
</code_context>
<issue_to_address>
**suggestion (performance):** Hardcoding `--num-workers 4` may underuse or oversubscribe CI runners; consider deriving it from available CPUs.

Fixing this at 4 assumes a specific runner size and may slow CI on larger machines or overload smaller ones. Instead, consider deriving the value from available CPUs (e.g. `--num-workers "$(nproc)"` on Linux) or omitting it and relying on mypy’s default unless you have data showing 4 is optimal.

```suggestion
      - name: Run mypy
        run: uv run --no-sync mypy --num-workers "$(nproc)"
```
</issue_to_address>

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