fix: support import subdirectory (#655)

.changeset/quick-fans-battle.md

examples/readers/src/assemblyai.ts

examples/readers/src/csv.ts

examples/readers/src/custom-simple-directory-reader.ts

examples/readers/src/docx.ts

examples/readers/src/html.ts

examples/readers/src/llamaparse.ts

examples/readers/src/markdown.ts

examples/readers/src/notion.ts

examples/readers/src/pdf.ts

examples/readers/src/pdf_fw.ts

examples/readers/src/pdf_fw_openai.ts

examples/readers/src/simple-directory-reader.ts

packages/core/package.json