API testing services implement concrete services

[ocket8888]

What this PR is primarily meant to do is make keeping parity between API services and their mock testing services easier for developers. It does this by, for each API service, ensuring it is implemented by the corresponding mock/testing service. For example, with the API service:

export class FooService extends APIService {
	//...
}

in experimental/traffic-portal/src/app/api, this PR ensures there is a corresponding service in experimental/traffic-portal/src/app/api/testing such that:

import { FooService as ConcreteFooService } from "../foo.service.ts";

export class FooService implements ConcreteFooService {
	//...
}

This means that adding functionality to the "concrete" service that isn't being properly mocked will result in testing compilation errors.

In order to ensure the services are working properly, this PR also adds 100% test coverage to experimental/traffic-portal/src/app/api/testing and fills any gaps in testing coverage for experimental/traffic-portal/src/app/api.

---

Which Traffic Control components are affected by this PR?

• Traffic Portal (experimental v2)

What is the best way to verify this PR?

Make sure the provided tests pass.

PR submission checklist

• This PR has tests
• This PR doesn't need documentation
• This PR doesn't need a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY

[codecov]

Codecov Report

❌ Patch coverage is 99.51456% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.60%. Comparing base (9cfe018) to head (1fed230).
⚠️ Report is 227 commits behind head on master.

Files with missing lines	Patch %	Lines
...tatuses/status-details/status-details.component.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             master    #7599       +/-   ##
=============================================
+ Coverage     31.83%   69.60%   +37.76%     
  Complexity       98       98               
=============================================
  Files           717      324      -393     
  Lines         82720    12865    -69855     
  Branches        965      974        +9     
=============================================
- Hits          26338     8955    -17383     
+ Misses        54217     3574    -50643     
+ Partials       2165      336     -1829     

Flag	Coverage Δ
golib_unit	?
grove_unit	?
t3c_unit	?
traffic_monitor_unit	?
traffic_ops_unit	?
traffic_portal_v2	83.78% <99.51%> (+9.38%)	⬆️
traffic_stats_unit	?
unit_tests	83.78% <99.51%> (+54.61%)	⬆️

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