v0.44.3

feat: expose --use_directml CLI flag (experimental) (#290)

* docs: design spec for exposing DirectML via CLI (experimental tier)

Contributor (Vageesha Gupta) reported DirectML support exists (PR #211)
but is unreachable from the CLI. Design: expose --use_directml as
explicit opt-in, add conditional discoverability hint, document as
experimental with an honest per-architecture status, ship a patch
release, and reply inviting validation of untested architectures.

* docs: implementation plan for DirectML CLI exposure + spec correction

Correct spec to drop remote-CLI scope: DirectML is local-only and the
remote separation servers run on CUDA/CPU, so plumbing use_directml
through audio_separator/remote/* would be dead config. Add 5-task TDD
plan (CLI flag, discoverability hint, README, version bump, reply draft).

* feat: expose --use_directml CLI flag (experimental)

Wire the existing Separator(use_directml=...) support (PR #211) to the
CLI, mirroring --use_autocast. Explicit opt-in only. Adds the fixture
key + a wiring test in test_cli.py.

* feat: hint that --use_directml is available when DML packages are installed

In the CPU-fallback path of setup_torch_device, if torch_directml or
onnxruntime-directml is installed but DirectML wasn't enabled, log a
one-line INFO hint pointing to --use_directml. Fires during
'audio-separator --env_info' on DirectML-capable machines.

* docs: add experimental DirectML (Windows AMD/Intel GPU) install section

New install section with the dml extra, --use_directml usage, env_info
confirmation line, and an honest per-architecture status matrix. Also
adds --use_directml to the ToC, the full CLI-options reference, and the
Separator class parameters list.

* chore: bump version to 0.44.3

* chore: drop internal planning docs from PR