#1585 - feat(better_networking): add structured response evaluator

[soumyarajbag]

PR Description

Closes #1585. Introduces a structured, pure-Dart response evaluation utility in the better_networking package.

The current codebase has no way to programmatically assert API response correctness — only visual inspection via the UI. This PR adds
evaluateResponse(), a pure function that takes an HttpResponseModel and a ResponseExpectation, and returns a typed List<EvalResult> —
one entry per configured assertion.

Supported assertions:

• statusCode — exact match against expected HTTP status
• maxLatency — response time within a duration threshold
• requiredJsonKeys — top-level JSON keys must be present in the body
• bodyContains — response body must contain a given substring
• contentType — Content-Type header must contain a given substring

Why this approach over a simple logger:

A void logger with side effects is untestable and throws away the result. Returning List<EvalResult> lets callers (UI, tests, future batch
eval) decide what to do with the outcome — display it, aggregate it, or fail a test.

final results = evaluateResponse(
  response,
  const ResponseExpectation(
    statusCode: 200,
    maxLatency: Duration(milliseconds: 500),
    requiredJsonKeys: ['id', 'name'],
    bodyContains: 'success',
    contentType: 'application/json',
  ),
);

// results → List<EvalResult> with .field, .passed, .expected, .actual, .message

This also serves as the foundation for the multimodal AI & Agent API Eval Framework (Idea #2), where batch evaluation requires running
per-response assertions across datasets.

Related Issues

• Closes Add basic evaluation logging for API responses #1585

Checklist

• I have gone through the contributing guide
• I have updated my branch and synced it with project main branch before making this PR
• I am using the latest Flutter stable branch (run flutter upgrade and verify)
• I have run the tests (flutter test) and all tests are passing

Added/updated tests?

• Yes
  • test/utils/response_evaluator_test.dart — 25 tests covering all 5 evaluation fields independently, edge cases (null body, null headers,
    null latency, empty keys list, long body truncation), and combined multi-assertion scenarios including result ordering

OS on which you have developed and tested the feature?

• Windows
• macOS
• Linux