Optimize OCI layout push blob to avoid file copy if already exists

[jonesbusy]

Description

Fix #185

Testing done

mvn clean install

Submitter checklist

• I have read and understood the CONTRIBUTING guide
• I have run mvn license:update-file-header, mvn spotless:apply, pre-commit run -a, mvn clean install before opening the PR

[codecov]

Codecov Report

❌ Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.55%. Comparing base (c4163b4) to head (9e7acdd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/main/java/land/oras/OCILayout.java	90.47%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #758      +/-   ##
============================================
+ Coverage     87.20%   87.55%   +0.34%     
- Complexity     1108     1109       +1     
============================================
  Files            45       45              
  Lines          3432     3446      +14     
  Branches        459      463       +4     
============================================
+ Hits           2993     3017      +24     
+ Misses          263      248      -15     
- Partials        176      181       +5     

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