[ascend]feat: support kv int8

[yao-fengchen]

Thanks for your contribution and we appreciate it a lot. The following instructions would make your pull request more healthy and more easily receiving feedbacks. If you do not understand some items, don't worry, just make the pull request and seek help from maintainers.

Motivation

This PR support kv int8 on ascend device.

Modification

This PR modified some paras in CacheEngine, context in model_forward，and op_backend of ascend.

BC-breaking (Optional)

Does the modification introduce changes that break the backward-compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit tests to ensure the correctness.
3. If the modification has a dependency on downstream projects of a newer version, this PR should be tested with all supported versions of downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[jinminxi104]

we will update docs for this pr in another pr

[grimoire]

what is ASCEND_QUANT_RECORD_FILE

[lvhan028]

we will update docs for this pr in another pr

why not put the doc in this PR?

[jinminxi104]

what is ASCEND_QUANT_RECORD_FILE

ascend only supports offline kv-quant。 ASCEND_QUANT_RECORD_FILE is the file contains all kv scales and offsets.
please refer this doc：https://github.com/DeepLink-org/dlinfer/blob/main/docs/quant/ascend_kv_quant.md

[jinminxi104]

we will update docs for this pr in another pr

why not put the doc in this PR?

doc updated