[release/2026930][Backport #40541] [NPU] Avoid FP8 dispatch for INT8 MoE on A5

[McZyWu]

Backport sgl-project#40541 to Ascend/sglang release/2026930 (base 282d4bbf2b).

Backport the A5 INT8 dispatcher fix only. The two indexer replay CI files changed upstream do not exist on this release branch, so their unrelated CI registration changes are omitted.

Validation on this backport:

• Python AST syntax, Ruff F401/F821/UP037 checks, and isort checks passed for all changed Python files.
• Ruff formatting checked; the adapted [NPU] Add opt-in MLA prefix FIA and Gemma norm fallback sgl-project/sglang#40131 test was formatted.
• Git diff whitespace checks passed.
• All four backports merge together without conflicts.
• Windows cannot run the complete runtime test suite because the Linux resource module is unavailable. NPU accuracy/performance tests were not rerun; upstream hardware results are historical, not release-branch validation.