Move torch/deepfilternet to optional [full] extra

Motivation

torch, torchaudio, and deepfilternet (~2GB+) are only used in the noise suppression path (noise_suppress=True), which is off by default. Every pip install openlrc currently pulls in these heavy dependencies even though most users only need transcription and translation.

Additionally, torchvision is declared as a dependency but never imported anywhere in the codebase.

Changes

pyproject.toml

• Move torch, torchaudio, and deepfilternet from dependencies to a new [project.optional-dependencies] full extra.
• Remove torchvision entirely (unused).

openlrc/preprocess.py

• Wrap import torch and from df.enhance import ... in noise_suppression() with a try/except ImportError that raises a clear message: "Install them with: pip install openlrc[full]".

openlrc/utils.py

• Make release_memory() gracefully handle missing torch (return early instead of crashing).
• Remove unused import torch from TYPE_CHECKING block.

.github/workflows/ci.yml

• Change uv run python -m unittest to uv run --extra full python -m unittest so CI continues to test the full feature set including noise suppression.

README.md

• Simplify installation steps: remove manual PyTorch, faster-whisper GitHub commit, and typing-extensions install instructions (no longer needed).
• Add step 5 documenting the optional pip install openlrc[full] for noise suppression.
• Update the Lightweight Imports note to reflect that the base install no longer includes torch.
• Annotate the noise_suppress=True code example with (requires openlrc[full]).

Migration

Existing users who rely on noise_suppress=True need to change their install command to pip install openlrc[full].