refactor: simplify track reader manager and messenger use

[TerryHowe]

What this PR does / why we need it:

If we just pass the messenger to reader, it will be a lot easier to test these packages.

Partial: #1461

[codecov]

Codecov Report

Attention: Patch coverage is 89.28571% with 9 lines in your changes missing coverage. Please review.

Project coverage is 86.06%. Comparing base (952d867) to head (f2066cc).

Files with missing lines	Patch %	Lines
cmd/oras/internal/display/status/track/target.go	69.23%	2 Missing and 2 partials ⚠️
cmd/oras/root/blob/fetch.go	62.50%	2 Missing and 1 partial ⚠️
cmd/oras/root/blob/push.go	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1474      +/-   ##
==========================================
+ Coverage   86.00%   86.06%   +0.05%     
==========================================
  Files         118      119       +1     
  Lines        4223     4269      +46     
==========================================
+ Hits         3632     3674      +42     
- Misses        353      355       +2     
- Partials      238      240       +2     

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[TerryHowe]

I'm going to make a couple PRs out of this until it is focused only one the reader/messenger refactor again.