mpegts: readd PCR to outgoing packets

[aler9]

this is needed to read H265 tracks with VLC+VDPAU hardware encoder (and is probably needed by other combinations too)

[codecov]

Codecov Report

Merging #74 (7256a6f) into main (e013434) will decrease coverage by 0.10%.
Report is 1 commits behind head on main.
The diff coverage is 92.05%.

@@            Coverage Diff             @@
##             main      #74      +/-   ##
==========================================
- Coverage   83.64%   83.55%   -0.10%     
==========================================
  Files          57       58       +1     
  Lines        4911     5016     +105     
==========================================
+ Hits         4108     4191      +83     
- Misses        589      608      +19     
- Partials      214      217       +3     

Files Changed	Coverage Δ
pkg/formats/mpegts/reader.go	66.88% <42.85%> (-1.15%)	⬇️
pkg/formats/mpegts/codec_mpeg4_video.go	75.00% <75.00%> (ø)
pkg/formats/mpegts/writer.go	91.54% <95.34%> (+0.73%)	⬆️
pkg/formats/mpegts/track.go	88.46% <100.00%> (+0.46%)	⬆️

... and 5 files with indirect coverage changes

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