fix: prevent stuck left mouse button in After Effects

[denizercealagoz]

Summary

• stop installing the no-op global event tap for primary mouse button events
• keep left/right mouse down and up events outside ButtonCore entirely
• retain the regression assertion that primary buttons are excluded from the dispatch mask

Why

Mos 4.0.2 installs a mutable global event tap for mouse-button events. Current master already moved primary clicks out of the mutable dispatch tap, but it still installs a separate listen-only tap whose callback only returns the original event.

Applications with their own drag state machines, notably Adobe After Effects, have been reported to enter a stuck left-click state while Mos is running. Since Mos does not record an unmodified primary click and the observation callback has no behavior, subscribing to those events adds input-path risk without providing functionality.

This change removes that remaining primary-button tap so Mos never observes or rewrites physical left/right clicks through ButtonCore.

Addresses #843.

Validation

• git diff --check
• xcrun swiftc -parse Mos/ButtonCore/ButtonCore.swift MosTests/InputProcessorTests.swift
• xcodebuild -scheme Debug -configuration Debug -destination 'platform=macOS' CODE_SIGNING_ALLOWED=NO build
• xcodebuild -scheme Debug -destination 'platform=macOS' CODE_SIGNING_ALLOWED=NO test -only-testing:MosTests/InputProcessorTests — 48 tests passed with 0 failures
• existing testButtonCore_dispatchEventMask_excludesPrimaryMouseButtons regression coverage passed
• runtime check on macOS 26.2 with Adobe After Effects 26.3.0: no stuck click observed during approximately 10–17 minutes of timeline/composition dragging and normal editing

Additional maintainer/community verification on other macOS and After Effects versions is welcome.