fix(core): honor explicit tenant access token when cache is enabled

[amdoi7]

Fixes #198

Summary

• keep WithTenantAccessToken(...) as the highest-priority tenant token source
• only fall back to tokenManager.getTenantAccessToken(...) when no explicit tenant token is provided
• add regression tests for both the explicit-token and cache-fallback paths

Root cause

In core/reqtranslator.go, the AccessTokenTypeTenant branch always called tokenManager.getTenantAccessToken(...) when EnableTokenCache=true, even if RequestOption.TenantAccessToken had already been set.

That meant an explicit tenant token could be silently overwritten by the cache/token-manager path.

Fix

Change the tenant token resolution logic from:

if config.EnableTokenCache {

to:

if config.EnableTokenCache && tenantAccessToken == "" {

This matches the existing AccessTokenTypeApp behavior and preserves the expected precedence:

• explicit tenant token
• cached/generated tenant token

Tests

Added:

• TestTranslate_ExplicitTenantAccessTokenBypassesCache
• TestTranslate_TenantAccessTokenUsesCacheWhenExplicitTokenMissing

Validated with:

go test ./core -run 'TestTranslate_(ExplicitTenantAccessTokenBypassesCache|TenantAccessTokenUsesCacheWhenExplicitTokenMissing)$'