Enhance blob storage functionality with file extension support

- Added an `Extension` field to `BlobMetadata` to store file extensions alongside existing metadata.
- Updated the `SaveBlob` method to handle file extensions, ensuring they are stored and retrieved correctly.
- Modified the `GetBlob` method to read blob data from the filesystem based on the stored extension.
- Enhanced the `Storage` struct to manage blob files in a specified directory, improving organization and access.
- Introduced utility functions for determining file extensions from MIME types, facilitating better file handling.
- Added comprehensive tests for new functionalities, ensuring robust behavior across blob operations.

pkg/blossom/blob.go

@@ -17,10 +17,11 @@ type BlobDescriptor struct {
 
 // BlobMetadata stores metadata about a blob in the database
 type BlobMetadata struct {
-	Pubkey   []byte `json:"pubkey"`
-	MimeType string `json:"mime_type"`
-	Uploaded int64  `json:"uploaded"`
-	Size     int64  `json:"size"`
+	Pubkey    []byte `json:"pubkey"`
+	MimeType  string `json:"mime_type"`
+	Uploaded  int64  `json:"uploaded"`
+	Size      int64  `json:"size"`
+	Extension string `json:"extension"` // File extension (e.g., ".png", ".pdf")
 }
 
 // NewBlobDescriptor creates a new blob descriptor
@@ -45,10 +46,11 @@ func NewBlobMetadata(pubkey []byte, mimeType string, size int64) *BlobMetadata {
 		mimeType = "application/octet-stream"
 	}
 	return &BlobMetadata{
-		Pubkey:   pubkey,
-		MimeType: mimeType,
-		Uploaded: time.Now().Unix(),
-		Size:     size,
+		Pubkey:    pubkey,
+		MimeType:  mimeType,
+		Uploaded:  time.Now().Unix(),
+		Size:      size,
+		Extension: "", // Will be set by SaveBlob
 	}
 }