feat: add Ascend950 TileLang and causal convolution support.

[wuyifan2017]

Description

• Resolve Ascend950 TileLang builds to dav-c310 and use the CANN-compatible A5 BiSheng flags.
• Pass device-specific compile flags through variant workers while preserving the existing A2/A3 --npu-arch path.
• Add the FP16 bs1_d6144_w4_silu0_f16 causal-conv variant used by Qwen3.5 decode.

Related Issues

N/A

Change Type

• Bug fix
• New feature
• Performance improvement
• Refactor
• Documentation
• Test
• Build or CI

Pull Request Checklist

Thank you for contributing to xLLM. Before requesting review, please make sure the following items are complete.

PR Title and Commit Messages

• The PR title and each commit message follow the xLLM commit format: <type>: <subject>.

Allowed types: feat, bugfix, docs, test, refactor, chore, style, revert, perf, model, build, release.
The subject should use clear English, start with a verb, include at least 4 words, and end with ..

Pre-commit Checks

• I have installed pre-commit by running pip install pre-commit or an equivalent command.
• I have installed the hooks with pre-commit install.
• I have run pre-commit run --all-files and fixed any reported issues.

If you are unsure how to set up pre-commit, see the pre-commit documentation.

Self Review

• I have self-reviewed the code according to .agents/skills/code-review/references/custom-code-style.md, especially code written or assisted by AI.
• I have rebased this PR onto the latest main branch.

Build and Test Coverage

• Tests have been added or updated as needed.
• CUDA: python setup.py build test has passed on a CUDA machine.
• NPU: python setup.py build test has passed on an NPU machine.
• MLU: python setup.py build test has passed on an MLU machine.

Reviewer Notes

• A focused Ascend950 AOT build passed for all five causal_conv1d variants, including bs1_d6144_w4_silu0_f16; generated manifests and object files report a5 / dav-c310.
• A2/A3 flag assertions confirm that both retained platforms still use the existing --npu-arch route.
• Python bytecode compilation and pre-commit run --all-files passed.