[ndabas]

As discussed in #519 -- this PR is stacked on top of #523 as JUCE added support for Windows ARM64 in 7.0.3. I can rebase this PR when that one is merged.

For the plugin binaries that are used for testing, I have added a workflow with a manual trigger, .github/workflows/build-windows-test-plugins.yml, which can build and optionally commit those files, either for ARM64 only or for x64 as well. Until those are committed, I added a commit which lowers the coverage minimum, only on Windows ARM64; this can be reverted or removed once the binaries are in. The build script also applies a couple of patches needed for JUCE 7:

• A Thread::Priority API change in the GUI library CHOWTapeModel bundles.
• A missing buffer.clear() in Magical8bitPlug2. Without it, output builds up from block to block under JUCE 7.

Some more notes:

• The Windows Python library path now comes from sys.base_prefix instead of a hard-coded x64 path.
• LAME's SSE switch is no longer forced on.
• Added windows-11-arm test jobs and win_arm64 wheels for Python 3.11–3.15. There is no ARM64 Windows build of Python 3.10.
• Tests: each plugin's binary architecture is checked, and plugin tests skip when no matching build exists.
• Plugin layout: the existing x64 plugins moved to .vst3/Contents/x86_64-win/.

All builds/tests pass (that workflow run is from a branch where I ran the VST build workflow so the binaries are on that branch, and I removed the coverage-reduction commit).

Closes #519.