Allow overriding protected methods on sfMusic and sfSoundStream

[Marioalexsan]

Fixes #394.

Implements overriding for protected methods in sfMusic and sfSoundStream by using the pattern described here.

The Chunk struct was also updated since the data types were different from the ones used in the C++ library:

// CSFML old struct
typedef struct
{
    int16_t*     samples;     ///< Pointer to the audio samples
    unsigned int sampleCount; ///< Number of samples pointed by Samples
} sfSoundStreamChunk;

// SFML's struct
struct Chunk
{
    const std::int16_t* samples{};     //!< Pointer to the audio samples
    std::size_t         sampleCount{}; //!< Number of samples pointed by Samples
};

Additionally, ci.yml was updated so that a newer version of CMake would be fetched. mirroring the current code in the SFML repo. Without this, CI would fail due to an unsupported old version (< 3.5) being fetched.

[eXpl0it3r]

Looking at sfSoundRecorder_create where we pass the callbacks directly, wouldn't that also be an option for sfSoundStream? Instead of separate callback function setters, they are set at creation.

Do we really want to provide overrides for sfMusic? Isn't that more comparable to sfSoundRecorder and sfSoundBufferRecorder? While we haven't marked sf::Music as final, there's rarely a point in extending it, as it's just a more fancy sf::SoundStream.