fix: add retry delay to WorldBank HTTP requests to handle transient 502 errors

The WorldBank type provider makes live HTTP requests at compile time to
populate the country/indicator/region/topic types. Previously, retries
happened immediately with no delay, meaning all 5 retries would fail in
rapid succession during transient server-side outages (e.g. 502 Bad Gateway).

Add a 2-second delay between retries so that brief API outages are more
likely to be survived before all retries are exhausted.

Fixes #1748

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

src/FSharp.Data.WorldBank.Core/WorldBankRuntime.fs

@@ -18,6 +18,7 @@ open FSharp.Data.Runtime.Caching
 module Implementation =
 
     let private retryCount = 5
+    let private retryDelayMs = 2000 // 2 seconds between retries to handle transient API failures (e.g. 502 Bad Gateway)
     let private parallelIndicatorPageDownloads = 8
 
     type internal IndicatorRecord =
@@ -85,6 +86,8 @@ module Implementation =
                         Debug.WriteLine(sprintf "[WorldBank] error: %s" (e.ToString()))
 
                         if attempt > 0 then
+                            // Delay before retrying to handle transient server-side failures (e.g. 502 Bad Gateway)
+                            do! Async.Sleep retryDelayMs
                             return! worldBankRequest (attempt - 1) funcs args
                         else
                             return! failwithf "Failed to request '%s'. Error: %O" url e