Fix test_text_decoder pytest collection collision

Summary:

examples/models/llama3_2_vision/text_decoder/test/ carried an empty
__init__.py while its parent text_decoder/ has none, so pytest derived the
module name test.test_text_decoder. That collides with the repo-root test/
package, which resolves the top-level test name first and has no
test_text_decoder submodule, producing:

  ModuleNotFoundError: No module named 'test.test_text_decoder'

This surfaced as a collection error in unittest / linux and
unittest-editable / linux, turning pull red on essentially every main commit
and blocking viable/strict promotion.

The __init__.py was empty boilerplate; the test uses only absolute imports and
no Buck target references the directory, so removing it is safe and lets pytest
import the module standalone.

Test Plan:

pytest examples/models/llama3_2_vision/text_decoder/test/test_text_decoder.py
CI: unittest / linux, unittest-editable / linux

Reviewers:

Authored with assistance from Claude Code.