Add Pyodide support (#12731)

This includes some initial work on adding Pyodide support (issue
#12729). It is enough to get
```
uv pip compile -p /path/to/pyodide --extra-index-url file:/path/to/simple-index
```
to work which should already be quite useful.

## Test Plan

* added a unit test for `pyodide_platform`
* integration tested manually with:
```
cargo run pip install \
-p /home/rchatham/Documents/programming/tmp/pyodide-venv-test/.pyodide-xbuildenv-0.29.3/0.27.4/xbuildenv/pyodide-root/dist/python \
--extra-index-url file:/home/rchatham/Documents/programming/tmp/pyodide-venv-test/.pyodide-xbuildenv-0.29.3/0.27.4/xbuildenv/pyodide-root/package_index \
--index-strategy unsafe-best-match --target blah --no-build \
numpy pydantic
```

---------

Co-authored-by: konsti <konstin@mailbox.org>
Co-authored-by: Zanie Blue <contact@zanie.dev>

crates/uv-python/src/platform.rs

@@ -348,6 +348,10 @@ impl From<&uv_platform_tags::Arch> for Arch {
                 ),
                 variant: None,
             },
+            uv_platform_tags::Arch::Wasm32 => Self {
+                family: target_lexicon::Architecture::Wasm32,
+                variant: None,
+            },
         }
     }
 }
@@ -380,6 +384,9 @@ impl From<&uv_platform_tags::Os> for Os {
             uv_platform_tags::Os::NetBsd { .. } => Self(target_lexicon::OperatingSystem::Netbsd),
             uv_platform_tags::Os::OpenBsd { .. } => Self(target_lexicon::OperatingSystem::Openbsd),
             uv_platform_tags::Os::Windows => Self(target_lexicon::OperatingSystem::Windows),
+            uv_platform_tags::Os::Pyodide { .. } => {
+                Self(target_lexicon::OperatingSystem::Emscripten)
+            }
         }
     }
 }