Switch to uv for dependency management and installation

[aviv1ron1]

Propose migrating the project's installation and dependency management workflow from pip + venv to uv.

Motivation:

• Speed — uv is significantly faster than pip for dependency resolution and installation, which matters given our multiple extras (compose, hf, vllm, vllm20, dev, dev-vllm20) and heavy dependencies like vLLM and Torch.
• Unified tooling — uv replaces venv, pip, and pip-tools with a single tool, simplifying onboarding.
• Reproducibility — uv produces a universal lockfile (uv.lock) for consistent environments across contributors and CI.
• Better extras handling — uv sync --extra cleanly handles our usecase-based installation pattern.
• Python version management — uv can manage Python versions itself, removing the need for separate pyenv setup.
• De-facto standard - uv us considered the de facto standard for pythion open source projects these days.

proposed readme after switch to uv:

# This project uses uv for dependency management.
# Install uv (one-time): https://docs.astral.sh/uv/getting-started/installation/

# Simple installation (base dependencies):
uv sync

# Or install with a specific usecase extra:
uv sync --extra compose      # Compose modular models
uv sync --extra hf           # HuggingFace inference
uv sync --extra vllm         # vLLM production inference (0.19.x)
uv sync --extra vllm20       # vLLM 0.20+ (requires CUDA 13+)
uv sync --extra dev          # Everything (uses vLLM 0.19.x by default)
uv sync --extra dev-vllm20   # Dev environment with vLLM 0.20+

[antonpibm]

Also related to #12
One thing that we need to verify is how the lock files behaves on different environments. We're highly affected by the GPU and CUDA versions available on the execution clusters, which in turn impose versioning restrictions on libraries so we must handle locking with care

[aviv1ron1]

the uv lock file will not require any change of behavior. it locks the versioning, not the variant.
the wheel variant gets resolved on installation time.
the same lock file will work for all machines