feat: adds a middleware to validate bucket/object names

Implements a middleware that validates incoming bucket and object names before authentication. This helps prevent malicious attacks that attempt to access restricted or unreachable data in `POSIX`.

Adds test cases to cover such attack scenarios, including false negatives where encoded paths are used to try accessing resources outside the intended bucket.

Removes bucket validation from all other layers—including `controllers` and both `POSIX` and `ScoutFS` backends — by moving the logic entirely into the middleware layer.

s3api/controllers/base.go

@@ -1720,14 +1720,6 @@ func (c S3ApiController) PutBucketActions(ctx *fiber.Ctx) error {
 			})
 	}
 
-	if ok := utils.IsValidBucketName(bucket); !ok {
-		return SendResponse(ctx, s3err.GetAPIError(s3err.ErrInvalidBucketName),
-			&MetaOpts{
-				Logger:     c.logger,
-				MetricsMng: c.mm,
-				Action:     metrics.ActionCreateBucket,
-			})
-	}
 	if ok := utils.IsValidOwnership(objectOwnership); !ok {
 		return SendResponse(ctx, s3err.APIError{
 			Code:           "InvalidArgument",