Use TorchX main from GitHub with dependency compatibility fixes

[hemildesai]

Summary

• switch torchx dependency to GitHub main (git+https://github.com/meta-pytorch/torchx.git@main)
• remove cryptography<43 pin and keep cryptography as a normal dependency
• keep uv overrides for cryptography and urllib3>=2.6.3
• add direct importlib-metadata dependency (was previously only transitive)
• add TorchX compatibility fixes for API changes on main:
  • nemo_run/run/logs.py: support torchx.util.colors with fallback to legacy module
  • nemo_run/run/torchx_backend/runner.py: support new _validate(..., cfg) signature with backward compatibility
• refresh uv.lock (TorchX now resolves from commit 029982c43d3b94a013be322d78d5dd2246542fe0)

Validation

• uv sync --extra skypilot succeeds and installs TorchX from GitHub main
• uv run --group lint -- ruff check passes
• uv run --group lint -- ruff format --diff passes
• targeted regressions pass:
  • uv run pytest test/run/test_experiment.py::test_experiment_dryrun_with_cleanup test/run/torchx_backend/test_api.py::test_run_dryrun_with_executor test/run/test_logs.py
• full CI-style pytest command run locally:
  • uv run -- coverage run --branch --source=nemo_run -a -m pytest
  • result: 1189 passed, 6 failed
  • remaining failures are environment-specific in this macOS workstation run:
    • 5 Docker scheduler tests fail without a running Docker daemon
    • 1 macOS tar metadata test (test_concatenate_tar_files_non_linux_integration) includes ._* files

[ko3n1g]

This breaks PyPi compatibility. We can use uv.sources to override with a vcs dependency in uv-environments only