[XPU] [Quant] rename mxfp8_e4m3_quantize and add xpu backend implementation

[zufangzhu]

1. Rename mxfp8_e4m3_quantize → flashinfer_mxfp8_e4m3_quantize to make it explicit that this path is implemented via FlashInfer (and avoid ambiguity with other backends).
2. Add xpu_mxfp8_quantize as a new custom op for XPU, providing an XPU MXFP8 quantization path.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @zufangzhu.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[gemini-code-assist]

Code Review

This pull request renames existing MXFP8 quantization functions to be FlashInfer-specific and introduces a new XPU-specific MXFP8 quantization implementation, including a custom operator registration. The review feedback identifies a critical type mismatch in the XPU fake implementation that would break torch.compile, as well as a non-idiomatic null check. Furthermore, the reviewer pointed out that the model executor still hardcodes FlashInfer calls, which will lead to runtime failures on XPU platforms, necessitating a platform-aware dispatch mechanism.

[mergify]

Hi @zufangzhu, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

Tip

Is mypy failing?

mypy is run differently in CI. If the failure is related to this check, please use the following command to run it locally:

# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10

[mergify]

Hi @zufangzhu, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

Tip

Is mypy failing?

mypy is run differently in CI. If the failure is related to this check, please use the following command to run it locally:

# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10

[mergify]

Hi @zufangzhu, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

Tip

Is mypy failing?

mypy is run differently in CI. If the failure is related to this check, please use the following command to run it locally:

# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10

[mergify]

Hi @zufangzhu, the pre-commit checks have failed. Please run:

uv pip install pre-commit>=4.5.1
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

Tip

Is mypy failing?

mypy is run differently in CI. If the failure is related to this check, please use the following command to run it locally:

# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10