Handle WaitForCacheSync failures for resources without watch support

[kaovilai]

Fixes #9381

Problem:
Velero's restore process ignores return values from WaitForCacheSync(),
causing error logs when informer caches fail to sync for API groups that
don't support watch operations (e.g., authorization.openshift.io/v1 on
OpenShift clusters). While restore operations complete successfully via
fallback to direct API calls, the error logs create confusion.

Solution:

• Track resources that fail to sync in resourcesWithoutInformerCache set
• Check WaitForCacheSync return values at two locations:
  1. Initial cache sync for all resources (restore.go:609-617)
  2. Per-resource sync for CRDs/RIA-added resources (restore.go:1070-1078)
• Bypass informer cache for tracked resources in getResource() (restore.go:1099)
• Use direct API calls via getResourceClient() for resources without cache
• Log informational messages (not errors) explaining API server restrictions

Testing:

• Added waitforcachesync_test.go with comprehensive unit tests
• Tests use generic example.com/v1/widgets to demonstrate pattern
• All existing restore package tests pass with no regressions

Impact:

• No functional changes - restore operations continue to work correctly
• Eliminates confusing error logs for expected API limitations
• Clear informational logging about cache bypass behavior
• Better handling of API groups with architectural watch restrictions

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com

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Fixes #(issue)

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• Accepted the DCO. Commits without the DCO will delay acceptance.
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[codecov]

Codecov Report

❌ Patch coverage is 64.70588% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.03%. Comparing base (45755e1) to head (458d8d7).

Files with missing lines	Patch %	Lines
pkg/restore/restore.go	64.70%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9384      +/-   ##
==========================================
- Coverage   60.03%   60.03%   -0.01%     
==========================================
  Files         384      384              
  Lines       35150    35165      +15     
==========================================
+ Hits        21103    21112       +9     
- Misses      12493    12498       +5     
- Partials     1554     1555       +1     

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[kaovilai]

moving to draft till we learn more about this problem.