Add support for specifying python_platform in pip_compile

[mark-thm]

uv 0.1.35 added the --python-platform option to uv pip compile:

      --python-platform <PYTHON_PLATFORM>
          The platform for which requirements should be resolved.

          Represented as a "target triple", a string that describes the target platform in terms of its CPU, vendor, and operating system
          name, like `x86_64-unknown-linux-gnu` or `aaarch64-apple-darwin`.

          Possible values:
          - windows:                    An alias for `x86_64-pc-windows-msvc`, the default target for Windows
          - linux:                      An alias for `x86_64-unknown-linux-gnu`, the default target for Linux
          - macos:                      An alias for `aarch64-apple-darwin`, the default target for macOS
          - x86_64-pc-windows-msvc:     An x86 Windows target
          - x86_64-unknown-linux-gnu:   An x86 Linux target
          - aarch64-apple-darwin:       An ARM-based macOS target, as seen on Apple Silicon devices
          - x86_64-apple-darwin:        An x86 macOS target
          - aarch64-unknown-linux-gnu:  An ARM64 Linux target
          - aarch64-unknown-linux-musl: An ARM64 Linux target
          - x86_64-unknown-linux-musl:  An x86_64 Linux target

In this PR, enable specifying any (or none) of these values using the python_platform arg in pip_compile.