fix: guard onError callback to prevent masking provider errors

[Copilot]

The onError callback in AbstractErrorHandlingCacheTagsProvider was unguarded—if it threw, it would mask the original provider error and bypass throwOnError/fallback behavior.

Changes

• Wrapped onError invocation in try-catch to isolate callback failures
• Log callback exceptions separately via console.error without affecting error flow
• Preserve deterministic behavior: original error is always thrown when throwOnError=true, fallback always returned when throwOnError=false

// Before: callback exception masks provider error
catch (error) {
  this.onError?.(error, { provider, method, args }); // throws → bypasses throwOnError
  if (this.throwOnError) throw error; // never reached
}

// After: callback exceptions isolated
catch (error) {
  try {
    this.onError?.(error, { provider, method, args });
  } catch (handlerError) {
    console.error(`Error handler itself failed in ${provider}.${method}.`, { handlerError });
  }
  if (this.throwOnError) throw error; // always executes correctly
}

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