CI: Emulator OOM kills system_server, causing Mono.Android.NET_Tests-NoAot to fail with no results

## Summary

The `Mono.Android.NET_Tests-NoAot` test component fails intermittently because the Android emulator runs out of memory, triggering the Low Memory Killer (LMK) to kill `system_server`. This causes a full system restart and kills the test app before any tests execute, producing no NUnit results.

**Failing build:** https://dev.azure.com/dnceng-public/public/_build/results?buildId=1362050&view=logs&j=b227c637-c968-57be-6c5e-9409267d8fb0&t=a68687ba-0089-5801-b54b-a3b240b66a93&l=6069

**Job:** `macOS > Tests > APKs 2` in the `Package Tests` stage (`dotnet-android` pipeline on `main`)

## Timeline from logcat

| Time | Event |
|------|-------|
| 16:06:22 | `am instrument` launches test app (PID 4181) |
| 16:06:24–29 | .NET runtime initializes normally (~5s), loads assemblies, resolves `NUnitInstrumentation` |
| 16:06:29.151 | **Last log from test app** — typemap resolution completed successfully |
| 16:06:29.823 | `Process 2922 exited due to signal 9 (Killed)` — LMK begins killing processes |
| 16:06:29–32 | **~80+ system services die** (`ServiceManager: service 'xxx' died`) |
| 16:06:32.302 | `lowmemorykiller: lmkd data connection dropped` — confirms OOM |
| 16:06:32.880 | `am instrument` process shuts down with no test results |

## Errors in build log

- `warning XAAADB0000: Failure [DELETE_FAILED_INTERNAL_ERROR]` — the prior uninstall also failed, suggesting the emulator was already unhealthy
- `error: Could not find NUnit2 results file after running component Mono.Android.NET_Tests/...NUnitInstrumentation: no nunit2-results-path bundle value found`
- `warning: Unable to process TestResult-Mono.Android.NET_Tests.xml. Is it empty? (Did a unit test runner SIGSEGV?)`

## Root cause

The emulator's Low Memory Killer killed `system_server`, which cascaded into a full system restart. The test app was killed as collateral damage before it could run any tests. This is a transient infrastructure issue, not a code bug.

## Suggestions for automatic CI recovery

### Option 1: Retry the test component on failure with no results

In `TestApks.targets`, when the `RunInstrumentationTests` task detects that no `nunit2-results-path` was returned (i.e. the app produced zero output), automatically retry the component once before reporting failure. This specifically targets the "emulator died" scenario without masking real test failures.

### Option 2: Add an emulator health check before running tests

Before launching `am instrument`, run a lightweight health-check (e.g. `adb shell getprop sys.boot_completed` + `adb shell am get-config`) and if the emulator is unresponsive or recently rebooted, restart it and re-deploy before running tests. This would catch the "already unhealthy" state indicated by the `DELETE_FAILED_INTERNAL_ERROR`.

### Option 3: Use Azure DevOps automatic retry for the job

Configure the `macOS > Tests > APKs 2` job with a `retryCountOnTaskFailure` so that Azure DevOps automatically retries the entire job on failure. This is the lowest-effort option but retries the full job rather than just the failing component.