feat: support uv with Android

[henryiii]

Now supported in the latest uv release.

[henryiii]

@mhsmith, does this seem reasonable? I'll be in India for a week, so feel free to edit as needed.

[mhsmith]

Looks good so far. A few comments:

• The docs say build[uv] will use uv "when making all build and test environments", but the current version of this PR still uses pip to install the test environment. This may be a problem if pip is not installed at all.

  To test this, the "frontend_good" test should probably be extended to include a test command.

• The Android references in the build-frontend docs should be updated. Suggest the following:

  uv currently does not support Windows on ARM,
  musllinux on s390x, AndroidPyodide, or iOS. Legacy dependencies like
  setuptools on Python < 3.12 and pip are not installed if using uv.

  On Android and Pyodide, only "build" isthe "pip" frontend is not supported.

[henryiii]

Looks like we need to translate pip's --platform into --python-platform on uv?

error: invalid value 'android_21_x86_64' for '--python-platform <PYTHON_PLATFORM>'
[possible values: windows, linux, macos, x86_64-pc-windows-msvc, aarch64-pc-windows-msvc, i686-pc-windows-msvc, x86_64-unknown-linux-gnu, aarch64-apple-darwin, x86_64-apple-darwin, aarch64-unknown-linux-gnu, aarch64-unknown-linux-musl, x86_64-unknown-linux-musl, riscv64-unknown-linux, x86_64-manylinux2014, x86_64-manylinux_2_17, x86_64-manylinux_2_28, x86_64-manylinux_2_31, x86_64-manylinux_2_32, x86_64-manylinux_2_33, x86_64-manylinux_2_34, x86_64-manylinux_2_35, x86_64-manylinux_2_36, x86_64-manylinux_2_37, x86_64-manylinux_2_38, x86_64-manylinux_2_39, x86_64-manylinux_2_40, aarch64-manylinux2014, aarch64-manylinux_2_17, aarch64-manylinux_2_28, aarch64-manylinux_2_31, aarch64-manylinux_2_32, aarch64-manylinux_2_33, aarch64-manylinux_2_34, aarch64-manylinux_2_35, aarch64-manylinux_2_36, aarch64-manylinux_2_37, aarch64-manylinux_2_38, aarch64-manylinux_2_39, aarch64-manylinux_2_40, aarch64-linux-android, x86_64-linux-android, wasm32-pyodide2024, arm64-apple-ios, arm64-apple-ios-simulator, x86_64-apple-ios-simulator]

[mhsmith]

Tests with a test command need to be decorated with @needs_emulator, so they'll be skipped on the CI platforms that don't support that.

But maybe this test doesn't need a test command at all. OK, I guess it does need one in order to check the test environment installed by uv. But this command doesn't actually use the environment.

[joerick]

Code looks good, but the CI failure seems relevant?