fix(#433): require EAP-TLS key and cert in builder

[cachebag]

• make EapOptionsBuilder::build() reject incomplete EAP-TLS configs
• require either private_key_path or private_key_blob
• require either client_cert_path or client_cert_blob
• add unit coverage for missing TLS private key and client certificate

This keeps the existing builder API unchanged and moves TLS required-field checks earlier, matching the builder docs.

[Copilot]

Pull request overview

This PR tightens validation in EapOptionsBuilder::build() so EAP-TLS configurations fail early when required TLS inputs are missing, aligning runtime behavior with the builder’s documented TLS example.

Changes:

• Reject EAP-TLS builds that omit both private_key_path and private_key_blob.
• Reject EAP-TLS builds that omit both client_cert_path and client_cert_blob.
• Add unit tests covering missing TLS private key and missing client certificate.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
nmrs/src/api/models/wifi.rs	Adds EAP-TLS-specific required-field validation during EapOptionsBuilder::build().
nmrs/src/api/models/tests.rs	Adds unit tests to ensure missing TLS key/cert are rejected with IncompleteBuilder.