Implement retry logic for HTTP requests with support for Retry-After header

[TingluoHuang]

Prepare for supporting Retry-After header on 429 response.

[Copilot]

Pull request overview

This PR updates the HTTP retry infrastructure to honor Retry-After on throttling responses (429), and wires that behavior into both the SDK retry handler and the runner’s action archive download path.

Changes:

• Added parsing/conversion of Retry-After into a retry delay and applied it in VssHttpRetryMessageHandler.
• Expanded default retryable HTTP status codes to include 429 TooManyRequests.
• Updated runner action archive download retry logic to prefer Retry-After when throttled.

Show a summary per file

File	Description
src/Sdk/WebApi/WebApi/OAuth/VssOAuthTokenHttpClient.cs	Adjusts retry option initialization for OAuth token HTTP calls.
src/Sdk/Common/Common/VssNetworkHelper.cs	Adds helper to parse Retry-After into a bounded retry delay.
src/Sdk/Common/Common/VssHttpRetryOptions.cs	Includes 429 TooManyRequests in default retryable status codes.
src/Sdk/Common/Common/VssHttpRetryMessageHandler.cs	Reads Retry-After and uses it to compute retry backoff.
src/Sdk/Common/Common/Utility/HttpHeaders.cs	Adds Retry-After header constant.
src/Runner.Worker/ActionManager.cs	Prefers Retry-After backoff for 429 during action archive download retries.
src/Runner.Sdk/Util/UrlUtil.cs	Adds GetRetryAfter helper to extract the header value.

Review details

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Suppressed comments (2)

src/Sdk/Common/Common/VssHttpRetryMessageHandler.cs:139

• Per-request retry option overrides are not fully honored here: max backoff is taken from m_retryOptions instead of the effective retryOptions for this request. This can produce a larger/smaller delay than the caller intended when overriding MaxBackoff.

                    // Honor the Retry-After header (delay in seconds or an absolute date/time) when present,
                    // otherwise fall back to the standard exponential backoff.
                    var retryAfterDelay = VssNetworkHelper.ConvertRetryAfterToTimeSpan(retryAfterHeader, minBackoff, m_retryOptions.MaxBackoff);
                    if (retryAfterDelay.HasValue)
                    {

src/Sdk/Common/Common/VssHttpRetryMessageHandler.cs:145

• Per-request retry option overrides are not fully honored: exponential backoff uses m_retryOptions.MaxBackoff/BackoffCoefficient instead of the effective retryOptions for this request.

                    {
                        backoff = BackoffTimerHelper.GetExponentialBackoff(attempt, minBackoff, m_retryOptions.MaxBackoff, m_retryOptions.BackoffCoefficient);
                    }

• Files reviewed: 7/7 changed files
• Comments generated: 4
• Review effort level: Lite