refactor(ai): ensure seperate I2V transcoding timeout

[rickstaa]

What does this pull request do? Explain your changes. (required)

This commit ensures a seperate I2V transcoding timeout. It also cleansup
the codebase a bit.

Specific updates (required)

How did you test each of these updates (required)

Does this pull request close any open issues?

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Project coverage is 36.08044%. Comparing base (e94b188) to head (91e4d9f).
Report is 12 commits behind head on ai-video.

Files with missing lines	Patch %	Lines
core/ai_worker.go	0.00000%	2 Missing ⚠️
cmd/livepeer/starter/starter.go	0.00000%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##            ai-video       #3219          +/-   ##
====================================================
- Coverage   50.82671%   36.08044%   -14.74627%     
====================================================
  Files            100         124          +24     
  Lines          23769       34509       +10740     
====================================================
+ Hits           12081       12451         +370     
- Misses         11018       21370       +10352     
- Partials         670         688          +18     

Files with missing lines	Coverage Δ
common/util.go	54.12541% <100.00000%> (-0.59772%)	⬇️
monitor/census.go	61.78046% <ø> (+0.20608%)	⬆️
cmd/livepeer/starter/starter.go	7.78715% <0.00000%> (ø)
core/ai_worker.go	35.64494% <0.00000%> (+0.63132%)	⬆️

... and 25 files with indirect coverage changes

---

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Files with missing lines	Coverage Δ
common/util.go	54.12541% <100.00000%> (-0.59772%)	⬇️
monitor/census.go	61.78046% <ø> (+0.20608%)	⬆️
cmd/livepeer/starter/starter.go	7.78715% <0.00000%> (ø)
core/ai_worker.go	35.64494% <0.00000%> (+0.63132%)	⬆️

... and 25 files with indirect coverage changes