Check hash of downloaded python toolchain

[j178]

Summary

Check the sha256 checksum when downloading a managed python toolchain.

Test Plan

$ cargo run -- python install 3.12

warning: `uv python install` is experimental and may change without warning.
Looking for installation Python 3.12.3 (any-3.12.3-any-any-any)
Downloading cpython-3.12.3-windows-x86_64-none
Installed Python 3.12.3 to C:\Users\jo\AppData\Roaming\uv\data\python\cpython-3.12.3-windows-x86_64-none
Installed 1 installation in 6s

$ cargo run -- python uninstall 3.12

$ # manually change the hash in `crates/uv-python/src/downloads.inc`

$ cargo run -- python install 3.12

warning: `uv python install` is experimental and may change without warning.
Looking for installation Python 3.12 (any-3.12-any-any-any)
Downloading cpython-3.12.3-windows-x86_64-none
error: Hash mismatch for `cpython-3.12.3-windows-x86_64-none`

Expected:
xx

Computed:
776568c92c5f3b47dbf5f17c1c58578f70d75a32654419a158aa8bdc6f95b09a

[zanieb]

Exciting to see this! Thank you :)

[zanieb]

@j178 Don't worry about those Windows stack overflows we're investigating that separately.

[charliermarsh]

Thanks, looks great! Tested it too.