feat: add gemini-2.0-flash-exp

[Laisky]

新增功能

增加对 gemini-2.0-flash-exp 的支持，不需要再手动修改部署的环境变量 GEMINI_VERSION 即可适配。

Bugfix

顺手修了长期存在的 bizErr 的 race 问题。将指针换成了结构体，防止 goroutine 内发生 race。

我已确认该 PR 已自测通过，相关截图如下

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 1.21%. Comparing base (7c8628b) to head (e507b30).

Files with missing lines	Patch %	Lines
relay/adaptor/gemini/adaptor.go	0.00%	5 Missing ⚠️
controller/relay.go	0.00%	3 Missing ⚠️
relay/adaptor/ollama/main.go	0.00%	3 Missing ⚠️
monitor/manage.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main   #1983      +/-   ##
========================================
- Coverage   1.21%   1.21%   -0.01%     
========================================
  Files        146     146              
  Lines      12295   12298       +3     
========================================
  Hits         149     149              
- Misses     12132   12135       +3     
  Partials      14      14              

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