Key TokenCache entries by auth provider identity, not just scope

[jonesbusy]

Description

Key TokenCache entries by auth provider identity, not just scope

Testing done

Let CI do it

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 92.10526% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.48%. Comparing base (b655d98) to head (13d5d0d).

Files with missing lines	Patch %	Lines
.../main/java/land/oras/auth/BearerTokenProvider.java	80.00%	2 Missing ⚠️
src/main/java/land/oras/auth/Scopes.java	95.45%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #826      +/-   ##
============================================
+ Coverage     86.95%   87.48%   +0.53%     
- Complexity     1261     1274      +13     
============================================
  Files            50       51       +1     
  Lines          4070     4091      +21     
  Branches        558      561       +3     
============================================
+ Hits           3539     3579      +40     
+ Misses          313      295      -18     
+ Partials        218      217       -1     

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