Push up pushIndex and prepare for reusable copy methods

[jonesbusy]

Push up pushIndex and prepare for reusable copy methods

Description

mvn clean install

Testing done

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

Attention: Patch coverage is 82.25806% with 11 lines in your changes missing coverage. Please review.

Project coverage is 84.97%. Comparing base (8df2896) to head (fc51669).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/main/java/land/oras/OCILayout.java	86.79%	4 Missing and 3 partials ⚠️
src/main/java/land/oras/LayoutRef.java	50.00%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #239      +/-   ##
============================================
- Coverage     85.53%   84.97%   -0.57%     
- Complexity      467      475       +8     
============================================
  Files            33       33              
  Lines          1542     1597      +55     
  Branches        175      184       +9     
============================================
+ Hits           1319     1357      +38     
- Misses          148      159      +11     
- Partials         75       81       +6     

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