Add credential vault SDKs and e2e coverage

[jwx0925]

Summary

• Add Credential Vault support to the Go, JavaScript, Kotlin/JVM, and C# sandbox SDK surfaces.
• Add SDK unit tests for Credential Vault models, adapters, and sandbox creation paths.
• Fold Credential Vault E2E coverage into the existing multi-language E2E jobs instead of keeping a separate Python-only job.
• Add Go, JavaScript, and JVM/Kotlin E2E cases matching the Python Credential Vault coverage, including all auth-type injection and runtime binding mutation.

Validation

• bash -n scripts/credential-vault-e2e-target.sh scripts/python-e2e.sh scripts/go-e2e.sh scripts/javascript-e2e.sh scripts/java-e2e.sh
• Parsed .github/workflows/real-e2e.yml with yaml.safe_load
• uv run ruff check tests/test_credential_vault_e2e.py
• uv run pytest tests/test_credential_vault_e2e.py -q
• GOCACHE=/private/tmp/opensandbox-go-build-cache go test ./... -run TestCredentialVault -count=1 -v
• corepack pnpm exec tsc --noEmit --target ES2022 --module NodeNext --moduleResolution NodeNext --allowImportingTsExtensions --strict tests/test_credential_vault_e2e.test.ts
• corepack pnpm exec eslint tests/test_credential_vault_e2e.test.ts
• corepack pnpm exec vitest run tests/test_credential_vault_e2e.test.ts
• Kotlin SDK and code-interpreter published to mavenLocal with JDK 17
• ./gradlew test --tests com.alibaba.opensandbox.e2e.CredentialVaultE2ETest -PskipCodeInterpreterE2E=true --rerun-tasks
• Shared-server live Credential Vault E2E passed for Python, Go, JavaScript, and JVM/Kotlin against one Kubernetes-backed OpenSandbox server
• BatchSandbox Vault examples passed for both private Git clone and GitLab API curl using Vault-injected credentials
• git diff --check

C# SDK unit tests were not run locally because dotnet is not installed in this environment.

[chatgpt-codex-connector]

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[hittyt]

LGTM