Fix RGBD loading in point cloud example

[dajiaohuang]

Summary

• restore the intended Reader.load_rgbd(True) call in the point-cloud example
• remove the unconditional ipdb breakpoint and discarded load_both() result
• ensure every later rgbd access refers to the frame loaded by the loop

Addresses #18.

Validation

• uvx ruff check --no-cache --select F821 --output-format concise examples/python/generate_pcd.py
• AST parse of all 15 tracked Python files
• structural assertion that load_rgbd assigns rgbd and no ipdb import remains
• python -m pytest -q -p no:cacheprovider python/tests/test_godot_depth_rgb_align.py python/tests/test_godot_spool_pack.py (16 passed, 1 skipped; the patched-FFmpeg integration test is skipped when that external environment is unavailable)

A full point-cloud run was not performed because it requires a built spatialmp4 extension plus the example's Open3D runtime and suitable capture input.

[DuinoDu]

LGTM

[dajiaohuang]

Thanks for the review. I also checked the red wheel run: the only failing leg stops in the repository's existing scripts/build_ffmpeg.sh while configuring FFmpeg (x265 not found using pkg-config), before this PR's package or example code is built. The remaining matrix legs were then cancelled by fail-fast. This PR does not change the workflow or build scripts, so I have not pushed an unrelated CI workaround here.