Validate mutual exclusion of StreamRoute sni and snis

Summary

Add ADC validation that rejects a stream route when both sni and snis are configured.

Rationale

The current schema and backend conversion paths can pass both fields to a backend. The gateway or API7 control plane rejects this invalid configuration. ADC should reject the configuration before it reaches a backend.

Affected areas

• TypeScript stream-route schema validation in libs/sdk/src/core/schema.ts
• Rust stream-route schema validation in rust/crates/adc-sdk/src/resources/route.rs
• Generated TypeScript and Rust schema artifacts, if required
• Validation tests for all supported backend write paths

Acceptance criteria

• ADC rejects any StreamRoute that sets both sni and snis.
• A route with only sni remains valid.
• A route with only snis remains valid.
• TypeScript and Rust validation tests cover the invalid and valid configurations.
• The configuration fails before backend-specific conversion or write operations.

Backlinks

• Pull request: https://github.com/api7/adc/pull/618
• Requesting comment: https://github.com/api7/adc/pull/618#issuecomment-5727794393
• Requested by: @bzp2010