Remove deprecated BYOC module from the Python SDK (superseded by live runner)

[rickstaa]

Context

byoc.py implements the legacy BYOC consumer flow (client-side sign + probabilistic micropayment for submit_byoc_job / submit_training_job) and is exported from the SDK via __init__.py. It was extended in #17 (merged), so it currently lives on main.

This consumer-side BYOC path is superseded by the live runner (#20, branch ja/live-runner), which becomes the supported way to get jobs onto the network. Shipping both leaves two overlapping job/payment paths on the public SDK surface.

Why

BYOC is deprecated and replaced by the live runner. Removing it collapses the SDK to a single job/payment path and drops the misleading public byoc API before v1.

Scope

• Delete src/livepeer_gateway/byoc.py.
• Remove the byoc imports and the matching __all__ entries (submit_byoc_job, submit_training_job, and the other byoc exports) from src/livepeer_gateway/__init__.py.
• Delete tests/test_byoc_refresh.py and tests/test_byoc_training.py.
• Keep remote_signer.py: it is shared and still imported by live_runner.py. Remove only BYOC-only paths if any remain after an audit.
• Verify no remaining byoc imports across src/ and examples/.

Preconditions (do not start until all are true)

• Live runner (Live Runner + Scope support #20) released.
• storyboard migrated off BYOC onto the live runner: https://github.com/livepeer/storyboard
• naap migrated off BYOC onto the live runner: https://github.com/livepeer/naap

Notes

• feat(byoc): sign + pay for submit_training_job, with P1-P3 tests #17 is already merged, so this is a removal of merged code, not a close-without-merge on the PR.

[linear-code]

ENG-128