Refactor DeveloperCertificateService to use ProcessSpec and ProcessUtil APIs with async/await

[Copilot]

Description

Refactors certificate trust checking methods to use repository's internal process execution APIs instead of directly creating ProcessStartInfo and calling Process.Start(), and converts synchronous methods to async for proper async/await patterns.

Changes:

• Replaced ProcessStartInfo with ProcessSpec for process configuration
• Replaced Process.Start() with ProcessUtil.Run() for process execution
• Converted IsCertificateTrusted to IsCertificateTrustedAsync with CancellationToken support
• Converted IsCertificateTrustedInMacOsKeychain to IsCertificateTrustedInMacOsKeychainAsync
• Replaced synchronous blocking calls (GetAwaiter().GetResult()) with proper async/await patterns
• Used await using for proper async disposal of IAsyncDisposable instead of try-finally with synchronous disposal
• Updated using statements: added Aspire.Hosting.Dcp.Process, removed System.Diagnostics
• Updated call site in DcpHost.cs to use the async method

Before:

var startInfo = new ProcessStartInfo { FileName = "security", ... };
using var process = Process.Start(startInfo);
process.WaitForExit();
return process.ExitCode == 0;

After:

var processSpec = new ProcessSpec("security") 
{
    Arguments = $"verify-cert -p basic -p ssl -c {certPath}",
    ThrowOnNonZeroReturnCode = false
};
var (task, processDisposable) = ProcessUtil.Run(processSpec);
await using (processDisposable.ConfigureAwait(false))
{
    var result = await task.WaitAsync(cancellationToken).ConfigureAwait(false);
    return result.ExitCode == 0;
}

This brings the code in line with process execution patterns and async/await best practices used throughout the rest of the Aspire.Hosting codebase.

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
  • No
• Does the change require an update in our Aspire docs?
  • Yes
  • No

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[danegsta]

@copilot update this method (and IsCertificateTrusted) to be async instead of calling GetAwaiter and synchronously resolving the task.

[Copilot]

Converted both methods to async in commit b7d5fcb:

• IsCertificateTrusted → IsCertificateTrustedAsync with CancellationToken support
• IsCertificateTrustedInMacOsKeychain → IsCertificateTrustedInMacOsKeychainAsync
• Replaced GetAwaiter().GetResult() with await task.WaitAsync(cancellationToken)
• Used await using for proper async disposal of IAsyncDisposable
• Updated call site in DcpHost.cs to use the async method