feat: support mounting blobs during copy

[qweeah]

What this PR does / why we need it:
This PR add mount support for oras cp.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1238

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ea47587) 81.55% compared to head (b4e1c24) 81.73%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1242      +/-   ##
==========================================
+ Coverage   81.55%   81.73%   +0.18%     
==========================================
  Files          68       68              
  Lines        3789     3806      +17     
==========================================
+ Hits         3090     3111      +21     
+ Misses        490      487       -3     
+ Partials      209      208       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[qweeah]

@ktarplee Can you help review if this implementation met the expected design of oras-project/oras-go#665

[ktarplee]

@ktarplee Can you help review if this implementation met the expected design of oras-project/oras-go#665

This looks great! I did not see any issues.

[shizhMSFT]

LGTM