feat(core): refactor linters config and improve code quality (#119)

- [x] Reorganize golangci-lint configuration with documented disable reasons
- [x] Simplify errcheck and revive linter rules with targeted exclusions
- [x] Pre-compile regex patterns in input_validation.go for performance
- [x] Fix type assertions in memory_shard.go and resp.go with safety checks
- [x] Replace string comparison with EqualFold for case-insensitive matching
- [x] Fix loop variable captures in jwk.go and logout.go
- [x] Change high goroutine log level from Info to Debug in autocleanup.go
- [x] Replace deprecated "cancelled" spelling with "canceled" throughout
- [x] Add nolint annotations for intentional unused parameters
- [x] Improve comment formatting for deprecated functions
- [x] Fix comment spelling: "marshalling" → "marshaling"
- [x] Refactor provider warnings formatting in internal/providers/warnings.go
- [x] Simplify metrics summary building in internal/recovery/metrics.go
- [x] Pre-allocate slice in error_recovery.go GetDegradedServices
- [x] Refactor context cancellation checks in redis.go

session.go

@@ -164,7 +164,7 @@ func decompressCombinedPayload(compressed string) (*combinedSessionPayload, erro
 	if err != nil {
 		return nil, fmt.Errorf("failed to create gzip reader: %w", err)
 	}
-	defer gr.Close()
+	defer func() { _ = gr.Close() }()
 
 	// Limit decompressed size to prevent zip bombs
 	limitedReader := io.LimitReader(gr, 512*1024) // 512KB max
@@ -1588,7 +1588,7 @@ func (sd *SessionData) returnToPoolSafely() {
 // Parameters:
 //   - r: The HTTP request context.
 //   - chunks: The map of session chunks (e.g., sd.accessTokenChunks) to clear and expire.
-func (sd *SessionData) clearTokenChunks(r *http.Request, chunks map[int]*sessions.Session) {
+func (sd *SessionData) clearTokenChunks(_ *http.Request, chunks map[int]*sessions.Session) {
 	for _, session := range chunks {
 		clearSessionValues(session, true)
 	}