Gemini token counting fixed; OAuth refresh hardened

What's Changed

• ci: protect _openapi_client from unauthorized changes by @KiewanVillatel in https://github.com/langchain-ai/langsmith-sdk/pull/2999
• fix: gemini double counting of over 200k tokens by @dqbd in https://github.com/langchain-ai/langsmith-sdk/pull/3003
• feat(python): cross-process OAuth refresh filesystem lock by @langchain-infra in https://github.com/langchain-ai/langsmith-sdk/pull/2988
• feat(js): cross-process OAuth refresh filesystem lock by @langchain-infra in https://github.com/langchain-ai/langsmith-sdk/pull/2989
• fix: avoid duplicate /v1 in hub URLs when endpoint includes /api/v1 by @langchain-infra in https://github.com/langchain-ai/langsmith-sdk/pull/3008
• chore: bump JS to 0.7.6 and Python to 0.8.12 by @langchain-infra in https://github.com/langchain-ai/langsmith-sdk/pull/3011

Full Changelog: https://github.com/langchain-ai/langsmith-sdk/compare/v0.8.11...v0.8.12