feat: use proto streams to increase maximum module files payload (#18268)

This PR implements protobuf streaming to handle large module files by:
1. **Streaming large payloads**: When module files exceed the 4MB limit,
they're streamed in chunks using a new UploadFile RPC method
2. **Database storage**: Streamed files are stored in the database and
referenced by hash for deduplication
3. **Backward compatibility**: Small module files continue using the
existing direct payload method

coderd/database/dbmem/dbmem.go

@@ -8743,6 +8743,12 @@ func (q *FakeQuerier) InsertFile(_ context.Context, arg database.InsertFileParam
 	q.mutex.Lock()
 	defer q.mutex.Unlock()
 
+	if slices.ContainsFunc(q.files, func(file database.File) bool {
+		return file.CreatedBy == arg.CreatedBy && file.Hash == arg.Hash
+	}) {
+		return database.File{}, newUniqueConstraintError(database.UniqueFilesHashCreatedByKey)
+	}
+
 	//nolint:gosimple
 	file := database.File{
 		ID:        arg.ID,