Guard optional UEFI dispatch registration

[zardus]

Follow-up to #702.

The merged cleanup registers singledispatch handlers whose annotations refer to uefi_firmware even when that optional dependency is unavailable. On Pyodide, importing CLE then fails while resolving those annotations.

This keeps the dependency-specific handlers and backend registration conditional, adds a subprocess regression test for importing without uefi_firmware, and selects the tandem PyVEX branch through tool.uv.sources.

[zardus]

Tandem PRs — please test these together:

• Support wasm32 hosts in VEX basic types vex#82
• Add wasm32 Pyodide wheel support pyvex#555
• Select the Pyodide Z3 build on Emscripten claripy#737
• Make native-only loaders optional on Emscripten #702
• Guard optional UEFI dispatch registration #703
• Test CLE under Pyodide #704
• Add Pyodide WebAssembly wheel support pypcode#283
• Add first-class WebAssembly runtime support angr#6658

[angr-bot]

Corpus decompilation diffs can be found at angr/dec-snapshots@master...angr/cle_703

[twizmwazin]

Can you also open a PR adding pyoxide CI akin to the pyvex one?

[zardus]

Opened #704 with Pyodide CI analogous to PyVEX. It builds the PyVEX WebAssembly wheel, installs CLE into a Pyodide virtualenv, and runs the CLE tests there.

[ltfish]

Thanks!