[Performance] Add retry with exponential backoff for ARM API throttling

[cocallaw]

Summary

Invoke-AzPagedRequest has no retry logic. Any 429 (throttled) or transient 5xx response immediately terminates pagination with a partial result set via Write-Error.

Impact

Multi-subscription Advisor queries are exactly the workload pattern that can hit ARM throttling limits. Users with many subscriptions may get incomplete results without clear indication that throttling was the cause.

Location

• Private/Invoke-AzPagedRequest.ps1 — paging loop catch block

Suggested fix

Add bounded retries with exponential backoff, honoring the Retry-After header when present:

$maxRetries = 3
$retryCount = 0

try {
    $response = Invoke-RestMethod -Uri $nextUri -Headers $Headers -Method Get -ErrorAction Stop
    $retryCount = 0  # Reset on success
}
catch {
    if ($retryCount -lt $maxRetries -and $_.Exception.Response.StatusCode -in @(429, 500, 502, 503, 504)) {
        $retryAfter = $_.Exception.Response.Headers["Retry-After"]
        $delay = if ($retryAfter) { [int]$retryAfter } else { [math]::Pow(2, $retryCount) }
        Write-Verbose "Throttled. Retrying in $delay seconds..."
        Start-Sleep -Seconds $delay
        $retryCount++
        continue
    }
    Write-Error "Azure API request failed for $nextUri: $_"
    return $results.ToArray()
}