Init indexed file

lib/idx/types.ts

@@ -0,0 +1,26 @@
+// src/index-file/types.ts
+export interface IndexHeader {
+  magic: string;
+  version: number;
+  createdAt: bigint;
+  entrySize: number;
+  entryCount: number;
+  validCount: number;
+  dataFileSize: bigint;
+  lastSequence: number;
+  reserved: Buffer;
+}
+
+export interface IndexEntry {
+  sequence: number;
+  timestamp: bigint;
+  offset: bigint;
+  length: number;
+  flags: number;
+  checksum: number;
+}
+
+export interface IndexFileOptions {
+  maxEntries: number;
+  magic?: string;
+}