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

jwk.go

@@ -213,9 +213,9 @@ func (jwk *JWK) ToECDSAPublicKey() (*ecdsa.PublicKey, error) {
 // GetKey finds a key by its ID (kid) in the JWKSet.
 // Returns nil if no key with the given ID is found.
 func (jwks *JWKSet) GetKey(kid string) *JWK {
-	for _, key := range jwks.Keys {
-		if key.Kid == kid {
-			return &key
+	for i := range jwks.Keys {
+		if jwks.Keys[i].Kid == kid {
+			return &jwks.Keys[i]
 		}
 	}
 	return nil