[mono] `System.Formats.Nrbf.Tests.EdgeCaseTests.CanReadArrayOfAnySize` times out on x64 Release Mono library legs

**Related runtime issues**: https://github.com/dotnet/runtime/issues/108515, https://github.com/dotnet/runtime/issues/110285, https://github.com/dotnet/runtime/issues/125994
**Related fix attempts**: https://github.com/dotnet/runtime/pull/126006, https://github.com/dotnet/runtime/pull/126189
**Suggested labels**: `Known Build Error`, `test-failure`, `arch-x64`, `area-Codegen-JIT-mono`, `area-System.Formats.Nrbf`, `untriaged`

## Build Information

Build: [20260405.1](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1367085), [20260405.15](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1367224), [20260406.2](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1367533), [20260406.53](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1367934), [20260407.4](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1368366), [20260407.63](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1368982)
Build error leg or test failing: `System.Formats.Nrbf.Tests.WorkItemExecution` / `System.Formats.Nrbf.Tests.EdgeCaseTests.CanReadArrayOfAnySize`
Affected CI jobs: `osx-x64 Release Mono_MiniJIT_LibrariesTests`, `linux-x64 Release Mono_MiniJIT_LibrariesTests`, `linux-x64 Release Mono_Interpreter_LibrariesTests`

## Error Message

Fill the error message using [step by step known issues guidance](https://github.com/dotnet/arcade/blob/main/Documentation/Projects/Build%20Analysis/KnownIssueJsonStepByStep.md).

```json
{
"ErrorMessage": [
"CanReadArrayOfAnySize",
"Executor timed out after 900 seconds and was killed"
],
"BuildRetry": false,
"ExcludeConsoleLog": false
}
```

## Summary

This is a recurrence of the existing `System.Formats.Nrbf.Tests` timeout history, not a brand-new failure mode.

Representative macOS and Linux Helix logs for the April 2026 bucket show the same pattern:

```text
Starting: System.Formats.Nrbf.Tests
System.Formats.Nrbf.Tests: [Long Running Test] 'System.Formats.Nrbf.Tests.EdgeCaseTests.CanReadArrayOfAnySize'
[EXECUTION TIMED OUT]
Exit Code:-3
Executor timed out after 900 seconds and was killed
```

Relevant prior tracking:

1. `dotnet/runtime#110285` captured the older broad KBE for `System.Formats.Nrbf.Tests` timeouts.
2. `dotnet/runtime#108515` narrowed the pattern to Mono x64 library legs, especially `linux_x64_release_mono_minijit_librariestests` and sometimes `linux_x64_release_mono_interpreter_librariestests`.
3. `dotnet/runtime#125994` named the exact test now showing up again in Helix logs: `System.Formats.Nrbf.Tests.EdgeCaseTests.CanReadArrayOfAnySize`.

Relevant fix attempts:

1. `dotnet/runtime#126006` tried to fix the timeout by skipping the 2 GB `Array.MaxLength` case on non-release runtimes.
2. `dotnet/runtime#126189` was a follow-up because `#126006` was incomplete; it tightened the condition so the large-case test requires not just a release runtime but also an optimized library.

Both PRs merged on 2026-03-27, before these 2026-04-05 through 2026-04-07 failures. That makes this bucket best understood as a recurrence / incomplete fix on Mono release jobs, not a fresh product regression.

The likely hot path remains `src/libraries/System.Formats.Nrbf/tests/EdgeCaseTests.cs`, specifically `CanReadArrayOfAnySize(int length)` with the `InlineData(2147483591)` (`Array.MaxLength`) case. A practical next step is to reopen or extend the Mono tracking in `#108515` and cross-link `#125994`, `#126006`, and `#126189`.

> [!NOTE]
> This issue was filed with the assistance of GitHub Copilot.

### Report

|Build|Repository|Test|Pull Request|
|---|---|---|---|
|[1577668](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1577668)|dotnet/runtime|[System.Formats.Nrbf.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1577668&view=ms.vss-test-web.build-test-results-tab&runId=43498368&resultId=240427)||
|[1558022](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1558022)|dotnet/runtime|[System.Formats.Nrbf.Tests.WorkItemExecution](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1558022&view=ms.vss-test-web.build-test-results-tab&runId=42880384&resultId=239486)||
#### Summary
|24-Hour Hit Count|7-Day Hit Count|1-Month Count|
|---|---|---|
|0|0|2|