refactor: Move channel write logic to manager

[TerryHowe]

What this PR does / why we need it:

Move these progress bar channel operations out of handler and into the manager.

[codecov]

Codecov Report

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.41%. Comparing base (d06bb81) to head (f16a833).

Files	Patch %	Lines
...d/oras/internal/display/status/progress/manager.go	75.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1445      +/-   ##
==========================================
- Coverage   85.46%   85.41%   -0.05%     
==========================================
  Files         108      108              
  Lines        3825     3827       +2     
==========================================
  Hits         3269     3269              
- Misses        332      334       +2     
  Partials      224      224              

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[qweeah]

LGTM, will check if SendAndStop helps refactoring Prompt usage next week.

[TerryHowe]

LGTM, will check if SendAndStop helps refactoring Prompt usage next week.

Sounds good. I was thinking there might be something there, but no clear vision of what right now.