chore: migrate Python type checking to ty (#8002)

## Summary
- replace Python lint type-checking from mypy to ty across LangGraph
packages
- remove mypy config/cache wiring and mypy-only references
- regenerate uv locks with ty 0.0.43

## Verification
- git diff --check
- make lint_package && make lint_tests in libs/langgraph
- make lint_package && make lint_tests in libs/checkpoint
- make lint_package && make lint_tests in libs/checkpoint-sqlite
- make lint_package && make lint_tests in libs/checkpoint-postgres
- make lint_package && make lint_tests in libs/prebuilt
- make lint_package && make lint_tests in libs/cli
- make lint in libs/sdk-py
- make lint in libs/checkpoint-conformance

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: open-swe[bot] <215916821+open-swe[bot]@users.noreply.github.com>

.github/workflows/_lint.yml

@@ -51,16 +51,6 @@ jobs:
         working-directory: ${{ inputs.working-directory }}
         run: uv sync --frozen --group lint
 
-      - name: Get .mypy_cache to speed up mypy
-        if: steps.changed-files.outputs.all || github.event_name == 'workflow_dispatch'
-        uses: actions/cache@v5
-        env:
-          SEGMENT_DOWNLOAD_TIMEOUT_MIN: "2"
-        with:
-          path: |
-            ${{ inputs.working-directory }}/.mypy_cache
-          key: mypy-lint-${{ runner.os }}-${{ runner.arch }}-py${{ matrix.python-version }}-${{ inputs.working-directory }}-${{ hashFiles(format('{0}/uv.lock', inputs.working-directory)) }}
-
       - name: Analysing package code with our lint
         if: steps.changed-files.outputs.all || github.event_name == 'workflow_dispatch'
         working-directory: ${{ inputs.working-directory }}
@@ -77,16 +67,6 @@ jobs:
         working-directory: ${{ inputs.working-directory }}
         run: uv sync --group lint
 
-      - name: Get .mypy_cache_test to speed up mypy
-        if: steps.changed-files.outputs.all || github.event_name == 'workflow_dispatch'
-        uses: actions/cache@v5
-        env:
-          SEGMENT_DOWNLOAD_TIMEOUT_MIN: "2"
-        with:
-          path: |
-            ${{ inputs.working-directory }}/.mypy_cache_test
-          key: mypy-test-${{ runner.os }}-${{ runner.arch }}-py${{ matrix.python-version }}-${{ inputs.working-directory }}-${{ hashFiles(format('{0}/uv.lock', inputs.working-directory)) }}
-
       - name: Analysing tests with our lint
         if: steps.changed-files.outputs.all || github.event_name == 'workflow_dispatch'
         working-directory: ${{ inputs.working-directory }}