refactor(storage): replace explicit upload/update variants with UploadMethod enum

Remove uploadMultipart, uploadResumable, updateMultipart, updateResumable and
consolidate into a method: UploadMethod parameter on upload() and update().

UploadMethod has three cases:
- .auto (default) — picks multipart for ≤6 MB, TUS for larger
- .multipart — always use a single multipart HTTP request
- .resumable — always use the TUS resumable protocol

update() now delegates to upload() internally, eliminating duplicated logic.
The private HTTP helper is renamed from uploadMultipart to _performMultipartRequest
to avoid confusion with the public API.

Updates docs, tests, and the FileUploadView example (adds method picker).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: grdsdev

Examples/Examples/Storage/FileUploadView.swift

@@ -24,6 +24,7 @@ struct FileUploadView: View {
   @State private var error: Error?
   @State private var upsertEnabled = false
   @State private var cacheControl = "3600"
+  @State private var uploadMethod: UploadMethod = .auto
 
   var body: some View {
     List {
@@ -59,6 +60,12 @@ struct FileUploadView: View {
             .keyboardType(.numberPad)
             .multilineTextAlignment(.trailing)
         }
+
+        Picker("Upload Method", selection: $uploadMethod) {
+          Text("Auto (size-based)").tag(UploadMethod.auto)
+          Text("Multipart").tag(UploadMethod.multipart)
+          Text("Resumable (TUS)").tag(UploadMethod.resumable)
+        }
       }
 
       Section("Upload from Photo Library") {
@@ -197,7 +204,7 @@ struct FileUploadView: View {
 
       let response = try await supabase.storage
         .from(selectedBucket)
-        .upload(filePath, data: imageData, options: options).value
+        .upload(filePath, data: imageData, options: options, method: uploadMethod).value
 
       uploadedPath = response.path
       uploadProgress = 1.0
@@ -235,7 +242,7 @@ struct FileUploadView: View {
 
       let response = try await supabase.storage
         .from(selectedBucket)
-        .upload(filePath, fileURL: selectedDocument, options: options).value
+        .upload(filePath, fileURL: selectedDocument, options: options, method: uploadMethod).value
 
       uploadedPath = response.path
       uploadProgress = 1.0
@@ -277,7 +284,7 @@ struct FileUploadView: View {
 
       let response = try await supabase.storage
         .from(selectedBucket)
-        .upload(filePath, data: data, options: options).value
+        .upload(filePath, data: data, options: options, method: uploadMethod).value
 
       uploadedPath = response.path
       uploadProgress = 1.0