Openaichat

[zichengorange]

📋 PR Title Format

feat(api): OpenAI advanced sampling params (logprobs, logit_bias, penalties)

📝 Change Type

Please select the type of change this PR introduces (choose one or more):

• [✅ ] feat: New feature.
• fix: Bug fix.
• docs: Documentation only changes.
• refactor: A code change that neither fixes a bug nor adds a feature.
• perf: Performance improvement.
• test: Adding missing tests or correcting existing tests.
• chore: Maintenance tasks (e.g., updating dependencies).

💡 Description

• logprobs / top_logprobs: 在采样后返回选中 token 的 logprob 及 top-k logprobs，并通过 HTTP API 以 OpenAI 兼容格式返回（含流式）。
• logit_bias: 支持对指定 token_id 加减 bias；bias=-100 时屏蔽该 token；超出 vocab 的 token_id 会忽略并打 Warning。
• presence_penalty / frequency_penalty: 在 softmax 前按历史 token 应用惩罚，用向量化实现。
• 容错: logprobs 计算异常时降级为不返回 logprobs，主线生成不受影响；API 层对异常 logprobs 做防御性处理。
• 同步修改 SamplingParams、forward.proto、executor、sampler、http_server，并增加 E2E 测试与本地验证文档。

✅ Checklist

Please ensure the following points are addressed before merging:

• [✅ ] I have performed a self-review of my own code.
• [✅ ] I have added/updated tests that prove my fix or feature works (if applicable).
• I have updated the documentation (if necessary).
• My code follows the project's style guidelines.