Dual-path retry: exponential backoff + CDN-driven httpConfig support

[MichaelGHSeg]

Summary

Rewrites HTTPClient.Upload() with a structured dual-path retry system and adds support for reading retry configuration from CDN settings (integrations["Segment.io"].httpConfig).

Retry logic (HTTPClient.cs)

• 429 + Retry-After header: sleep for the specified duration, does NOT consume the retry budget. Bounded by MaxRateLimitRetries and MaxRateLimitDuration (default 12h). Retry-After: 0 is treated as a 1-second floor to prevent busy-loops.
• Other retryable errors (5xx, 408, 410, 460): counted exponential backoff (base 500ms, 2×, cap 60s). Bounded by MaxRetries and MaxTotalBackoffDuration (default 12h).
• Non-retryable errors: discard immediately.
• Returns true on all terminal failure paths so EventPipeline removes the batch file instead of re-uploading indefinitely.
• New configurable properties: MaxRetries, MaxRateLimitRetries, BackoffEnabled, RateLimitEnabled, BaseBackoffMs, MaxBackoffMs, MaxRetryAfterCapSeconds, StatusCodeOverrides.
• Adds X-Retry-Count header on retry attempts.

CDN-driven config (SegmentDestination.cs)

• Reads httpConfig.backoffConfig and httpConfig.rateLimitConfig from CDN settings and applies them to the HTTP client after settings arrive.
• statusCodeOverrides uses dynamic key enumeration (matching the analytics-kotlin approach) instead of a hardcoded status code list — any valid HTTP status code (100–599) in the CDN config is respected.
• Uses CultureInfo.InvariantCulture for double.TryParse to handle non-English locales correctly.
• Maps maxRetryInterval to MaxRetryAfterCapSeconds (per-request sleep cap, not total budget).

E2E cli (e2e-cli/)

• CapturingLogger filters to final-failure messages only ("Retries exhausted", "Max total backoff") to avoid false failures from transient per-attempt errors.
• Uses enrichment callbacks for userId injection instead of pre-calling Identify.
• Adds 2s wait after new Analytics() when AUTO_SETTINGS=true so CDN settings arrive before the first upload.
• Enables retry and retry-settings test suites.

Test plan

• dotnet test passes
• E2E basic,retry,retry-settings suites pass (68/68)