fix(azure): normalize endpoint trailing slashes

[HAYDEN-OAI]

Summary

• normalize AzureOpenAI endpoints before appending /openai
• add a focused regression test for the documented trailing-slash endpoint form

Why

AzureClientOptions.endpoint is documented with a trailing slash, but the constructor appended /openai directly. Passing the documented form produced a base URL such as https://example-resource.azure.openai.com//openai, which then carried the double slash into Azure request URLs.

Impact

new AzureOpenAI({ endpoint: 'https://example-resource.azure.openai.com/' }) now produces https://example-resource.azure.openai.com/openai. Endpoints without trailing slashes and callers that provide an explicit baseURL keep their existing behavior.

Fixes #1669.

Validation

• pnpm exec jest tests/lib/azure.test.ts --runInBand
• pnpm exec prettier --check src/azure.ts tests/lib/azure.test.ts
• pnpm run lint

[openai-sdks]

OkTest Summary

❌ Failed for Node SDK PR #1995.

View OkTest run #29291098950

_{SDK merge (518fe091ab5e) · head (a6d54948d2be) · base (1cdc0196b434) · OkTest (cb7f0514ccd2)}