Dynamic FPS selection on DFXPReader

[Marcelpv96]

The methods _convert_clock_time_to_microseconds and _convert_time_count_to_microseconds are fixed to 30fps.

The modified code uses 30fps by default but also looks for an alternative frame rate on the CloseCaption file.

[mnc537]

Hello @ana-nichifor! Can you take a look to this? I'm reading closed captions at 23.976 fps and the result is drifted as a consequence of that 30fps manually set.

[OlteanuRares]

Hi @Marcelpv96, thanks for this PR — the fix is valid and addresses a real issue with frame-based timestamp drift on non-30fps content.
We'd like to merge this, but the branch has conflicts with current main (formatting changes since 2022).
The approach and logic are sound though.
Are you still interested in updating this PR? If so, here's what's needed:

• Rebase onto current main to resolve conflicts
• The two / 30 replacements and _get_framerate logic are correct as-is

If you're no longer available to update it, let us know and we'll cherry-pick the logic into a fresh branch. Either way, we want to get this in.
Thanks!