Update codebase to Zig 0.15.2

[asessa]

- Updated build.zig and build.zig.zon for Zig 0.15.2 compatibility
- Updated example/build.zig and example/build.zig.zon
- Updated source files to use new Zig 0.15.2 API:
  - bucket.zig, consts.zig, cursor.zig, db.zig
  - freelist.zig, gc.zig, node.zig, pretty_table.zig - tests.zig, tx.zig, util.zig

[laohanlinux]

Please also update ci zig version to 0.15.2