[bugfix] Fix FluxSamplingParam import path after configs/sample → api rename

fastvideo/api/flux.py still imported SamplingParam from
fastvideo.configs.sample.base (old path removed on main), causing a
ModuleNotFoundError at import time. Updated to fastvideo.api.sampling_param.

Author: Mister-Raggs

fastvideo/api/flux.py

@@ -4,7 +4,7 @@
 
 from dataclasses import dataclass
 
-from fastvideo.configs.sample.base import SamplingParam
+from fastvideo.api.sampling_param import SamplingParam
 
 
 @dataclass