Even tough the sound visualizer has `channels` as one of its parameters
it wasn't using it properly.
### Problem description
The biggest problem is that at each frame the index was being advanced
per channel frame_count increments. The number of channels also
determines how many graph will be needed to display the graphs of the
visualized sound files. Besides these two problems there were many
others like incorrect playback time, cracking audio, etc. which will not
be mentioned.
### Implementation description
To sample the signal a channel sampler was created based on the one used
previously that returns as many sampled signals as there are channels.
This PR aims hopefully at fixing all the problems encountered, and it
has been tested extensively using `Audacity` exported samples to ensure
the visualizer fidelity on playback and graph appearance.
### Screenshots
* build: Experimentally switch to gcc on macOS
* build: Corrected gcc paths
* build: Enable objective c support on macOS
* build: Enable ObjC and ObjC++ on macOS
* build: Add ObjC and ObjC++ flags
* build: Try compiling objc with clang
* build: Remove invalid flags again
* fix: Let's not include objc headers in C++ code
* sys: Move macos utils code to its own file
* fix: Missing unistd include on mac
* sys: Removed loader script stuff since it's currently unused and broken
* fix: Missing include
* fix: Another missing include
* fix: CFURLCreateWithBytes wants a pointer to mutable data
* fix: Try disabling name mangling of ObjC functions
* sys: Move macos utils declarations to its own header file
* fix: C Linkage
* fix: Move objc function prototypes to C++ headers
* fix: More missing includes
* fix: Warning error
* sys: Call ObjC with C ABI instead of trying to use C++
* build: Update libraries
* sys: Fixed build errors
* sys: No const correctness I guess
* sys: Fixed prototypes
* sys: This is C now
* sys: More nullptr -> NULL
* sys: Fix crash on exit
* sys: Try using proper std concepts instead of custom ones
* sys: Replaced another hex::is_signed
* build: Upgrade to gcc 12 and MacOS Monterey
* build: Fixed MacOS runner name
* build: Cache correct ccache folder on macOS
