Fix broken import/export mappings in npm package

Remove hash: false from the second tsdown build configuration (tests)
to prevent test chunk files from overwriting the main package chunks.

When both builds used hash: false, they generated chunks with the same
names (e.g., types.js). The second build overwrote the first build's
chunks, causing import/export mismatches at runtime with errors like:
"The requested module '../types.js' does not provide an export named 'i'"

This was a regression introduced in version 1.6.14.

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