Add Blossom package with core functionalities for blob storage and authorization

- Introduced the Blossom package, implementing essential features for handling blob storage, including upload, retrieval, and deletion of blobs.
- Added authorization mechanisms for secure access to blob operations, validating authorization events based on Nostr standards.
- Implemented various HTTP handlers for managing blob interactions, including GET, HEAD, PUT, and DELETE requests.
- Developed utility functions for SHA256 hash calculations, MIME type detection, and range request handling.
- Established a storage layer using Badger database for efficient blob data management and metadata storage.
- Included placeholder implementations for media optimization and payment handling, setting the groundwork for future enhancements.
- Documented the new functionalities and usage patterns in the codebase for better maintainability and understanding.

pkg/blossom/blob.go

@@ -0,0 +1,65 @@
+package blossom
+
+import (
+	"encoding/json"
+	"time"
+)
+
+// BlobDescriptor represents a blob descriptor as defined in BUD-02
+type BlobDescriptor struct {
+	URL      string     `json:"url"`
+	SHA256   string     `json:"sha256"`
+	Size     int64      `json:"size"`
+	Type     string     `json:"type"`
+	Uploaded int64      `json:"uploaded"`
+	NIP94    [][]string `json:"nip94,omitempty"`
+}
+
+// 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"`
+}
+
+// NewBlobDescriptor creates a new blob descriptor
+func NewBlobDescriptor(
+	url, sha256 string, size int64, mimeType string, uploaded int64,
+) *BlobDescriptor {
+	if mimeType == "" {
+		mimeType = "application/octet-stream"
+	}
+	return &BlobDescriptor{
+		URL:      url,
+		SHA256:   sha256,
+		Size:     size,
+		Type:     mimeType,
+		Uploaded: uploaded,
+	}
+}
+
+// NewBlobMetadata creates a new blob metadata struct
+func NewBlobMetadata(pubkey []byte, mimeType string, size int64) *BlobMetadata {
+	if mimeType == "" {
+		mimeType = "application/octet-stream"
+	}
+	return &BlobMetadata{
+		Pubkey:   pubkey,
+		MimeType: mimeType,
+		Uploaded: time.Now().Unix(),
+		Size:     size,
+	}
+}
+
+// Serialize serializes blob metadata to JSON
+func (bm *BlobMetadata) Serialize() (data []byte, err error) {
+	return json.Marshal(bm)
+}
+
+// DeserializeBlobMetadata deserializes blob metadata from JSON
+func DeserializeBlobMetadata(data []byte) (bm *BlobMetadata, err error) {
+	bm = &BlobMetadata{}
+	err = json.Unmarshal(data, bm)
+	return
+}