[cscore] Fix USB video mode handling on macOS

[yuhao1118]

Fix UsbCameraImpl on macOS

Changes

1. Removed redundant m_mode member variable from UsbCameraImpl class

   • The local m_mode was shadowing the parent class's m_mode from SourceImpl
   • This prevented proper read/write access to the parent's m_mode, causing incorrect GetVideoMode return values

2. Improved FPS validation logic in deviceCheckModeValid

   • Previously only checked the first matching VideoMode for FPS compatibility
   • Now checks all VideoModes with matching resolution and pixel format
   • This fixes cases where multiple VideoModes with different FPS ranges exist for the same resolution/pixel format

Testing

• Verified that GetVideoMode now returns correct values
• Confirmed that FPS validation works correctly for all supported video modes

[yuhao1118]

@peterjohns Hi, can I request for a CR about this PR? Thanks!

[sciencewhiz]

Hi, can I request for a CR about this PR? Thanks!

With the FRC Championship happening right now, the WPILib team has other priorities, so it might be a little while.

[ThadHouse]

Looks Great.

macOS support was definitely written a bit hacky. Mainly because its basically broken if used from robot programs in sim, due to thread requirements. But for UI tools, it should work fairly well.