Add LoadSoundFromPhysFS()

[RobLoach]

Summary

The README advertises loading "sounds" from archives, but there is no LoadSoundFromPhysFS(). Callers (including our own example examples/audio/audio_sound_loading.c, lines 31–35) must manually do:

Wave wav = LoadWaveFromPhysFS("res/sound.wav");
Sound fx = LoadSoundFromWave(wav);
UnloadWave(wav);

Every other common raylib file loader has a ...FromPhysFS counterpart (LoadImageFromPhysFS, LoadTextureFromPhysFS, LoadWaveFromPhysFS, LoadMusicStreamFromPhysFS, LoadFontFromPhysFS, LoadShaderFromPhysFS). LoadSound() is the missing obvious one.

Proposed API

RAYLIB_PHYSFS_DEF Sound LoadSoundFromPhysFS(const char* fileName);  // Load a sound from PhysFS

Suggested Implementation

In raylib-physfs.h, next to LoadWaveFromPhysFS():

Sound LoadSoundFromPhysFS(const char* fileName) {
    Wave wave = LoadWaveFromPhysFS(fileName);
    if (wave.data == NULL) {
        Sound output = { 0 };
        return output;
    }
    Sound sound = LoadSoundFromWave(wave);
    UnloadWave(wave);
    return sound;
}

• Add the declaration to the header block and the README API list.
• Simplify examples/audio/audio_sound_loading.c to use it.

QA

• New test in test/raylib-physfs-test.c — note LoadSoundFromWave() needs the audio device only for playback in some raylib versions; if headless CI can't validate the Sound, at minimum assert the missing-file path returns a zeroed Sound (AssertEqual(sound.stream.buffer, 0)), mirroring the existing LoadWaveFromPhysFS missing-file test at test/raylib-physfs-test.c:162.
• Example still builds and plays both WAV and OGG.

Context

• Distinct from open issue Write-side parity: ExportImageToPhysFS / ExportWaveToPhysFS / ExportImageAsCodeToPhysFS #34 (write-side Export* parity) — this is read-side parity.
• Model/automation loaders are tracked separately in Add LoadModelFromPhysFS() #17, Add LoadModelAnimationFromPhysFS() #18, Add LoadMaterialsFromPhysFS() #19, Add LoadAutomationEventListFromPhysFS() #21; this issue is intentionally scoped to LoadSound only.
• From a planning pass on 2026-07-20. No dependencies; small standalone change.