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 82.40741% with 19 lines in your changes missing coverage. Please review.

Project coverage is 85.42%. Comparing base (5792c35) to head (6d7282d).

Files	Patch %	Lines
...md/oras/internal/display/status/console/discard.go	80.00%	6 Missing ⚠️
...md/oras/internal/display/status/console/console.go	83.33%	2 Missing and 2 partials ⚠️
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   85.54%   85.42%   -0.12%     
==========================================
  Files         113      114       +1     
  Lines        3936     3986      +50     
==========================================
+ Hits         3367     3405      +38     
- Misses        342      350       +8     
- Partials      227      231       +4     

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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.