FIX: Audio files content check bug

[jbolor21]

Description

Sending audio files ie via Realtime is failing with the GUI because the whole base64 is being read by Path(piece.original_value).is_file(), which treats the whole string as a potential filename, which obviously is too long and thus errors out.
As a fix, this adds two guards:

1. Length check (< 4096) — no real filesystem path is that long, so skip the check for base64 data
2. try/except OSError — catch any remaining edge cases where the OS rejects the path

This lets the base64 audio data flow through to the serializer where it gets properly decoded and saved as a .wav file.

Tests and Documentation

Tested manually via UI and reran all tests and added new unit test

[behnam-o]

nit: I think the length check is unnecessary, and also I suggest you don't need to the extra variable is_existing_file, which is set in the try/catch block and used [only] right after it. instead, this might be more readable:

(basically just add a try: <current-code> except (OSError): <pass>

try:
    if Path(piece.original_value).is_file():
        if piece.converted_value is None:
            piece.converted_value = piece.original_value
        continue
except (OSError, ValueError):
    pass

This will take care of cases where the content is indeed resolvable to a file, and pass over it when it's not.