rewrite R2 publishing in Python (#1051)

This rips out the mirror uploading logic from the `pythonbuild` rust CLI
and moves it to Python, mainly because the rust aws sdk is clearly not
mature enough to support our use case, as evidenced by
#1047

I've also had to start using `--no-dev` on some existing `uv run`
invocations because `moto` wouldn't cleanly install in some build jobs
(like when building CPython for Windows).

## Test plan

Apart from unit tests, there's now an integration test with a local,
mocked S3 provider (using `moto`).

Dry run release on this branch:
https://github.com/astral-sh/python-build-standalone/actions/runs/23550742376

Author: zsol

.github/workflows/check.yml

@@ -30,3 +30,11 @@ jobs:
       - name: "Run checks"
         run: |
           ./check.py
+
+      - name: "Run unit tests"
+        run: |
+          uv run python -m unittest tests/test_mirror.py
+
+      - name: "Run mirror integration test"
+        run: |
+          uv run python -m unittest tests/test_mirror_integration.py

.github/workflows/release.yml

@@ -45,6 +45,8 @@ jobs:
           repo: casey/just
           version: 1.42.4
 
+      - uses: astral-sh/setup-uv@37802adc94f370d6bfd71619e3f0bf239e1f3b78 # v7.6.0
+
       # Perform a release in dry-run mode.
       - run: just release-dry-run ${GH_TOKEN} ${GITHUB_EVENT_INPUTS_SHA} ${GITHUB_EVENT_INPUTS_TAG}
         if: ${{ github.event.inputs.dry-run == 'true' }}

.github/workflows/windows.yml

@@ -150,7 +150,7 @@ jobs:
       # don't get compiled properly.
       - name: Bootstrap Python environment
         run: |
-          uv run build.py --help
+          uv run --no-dev build.py --help
 
       - name: Build
         if: ${{ ! matrix.dry-run }}
@@ -161,7 +161,7 @@ jobs:
           ) ELSE (
             call "C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Auxiliary\Build\%MATRIX_VCVARS%"
           )
-          uv run build.py --python cpython-%MATRIX_PYTHON% --sh c:\cygwin\bin\sh.exe --options %MATRIX_BUILD_OPTIONS% --vs %MATRIX_VS_VERSION%
+          uv run --no-dev build.py --python cpython-%MATRIX_PYTHON% --sh c:\cygwin\bin\sh.exe --options %MATRIX_BUILD_OPTIONS% --vs %MATRIX_VS_VERSION%
         env:
           MATRIX_VCVARS: ${{ matrix.vcvars }}
           MATRIX_PYTHON: ${{ matrix.python }}