Resolve LinearBase circular import

[zhengy001]

Motivation

Resolve the following import error by lazy import. Mainly from this PR: vllm-project/vllm@388ee3d

import sglang
import sglang.srt.models.phi3_small

ImportError: cannot import name 'LinearBase' from partially initialized module 'sglang.srt.layers.linear' (most likely due to a circular import)

Modifications

Checklist

• Format your code according to the Code Formatting with Pre-Commit.
• Add unit tests as outlined in the Running Unit Tests.
• Update documentation / docstrings / example tutorials as needed, according to Writing Documentation.
• Provide throughput / latency benchmark results and accuracy evaluation results as needed, according to Benchmark and Profiling and Accuracy Results.
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[zhaochenyang20]

Thanks. This looks good to me. Could @FrankLeeeee Take a look?