chore(scripts): harden bench suite report capture

Speedtest failures print an exit-code note instead of an empty section,
the report file writes progressively again (utf8 rewrite at the end),
and pytest-asyncio's py3.14 deprecation warning is filtered.

pyproject.toml

@@ -116,6 +116,7 @@ filterwarnings = [
     "ignore::DeprecationWarning:ast",
     "ignore::aiohttp.web_exceptions.NotAppKeyWarning",
     "ignore::DeprecationWarning:pycaption.*",
+    "ignore::DeprecationWarning:pytest_asyncio.*",
     "ignore::bs4.XMLParsedAsHTMLWarning",
 ]
 addopts = "-ra --strict-markers"

scripts/bench_suite.ps1

@@ -48,6 +48,7 @@ function Run($a) {
     # (e.g. "2Gbe -> ~1900 Mbps expected ceiling"). Uses whatever CLI exists.
     Write-Output ""
     Write-Output "==================== speedtest baseline ===================="
+    $global:LASTEXITCODE = 0
     if (Get-Command speedtest -ErrorAction SilentlyContinue) {
         & speedtest --accept-license --accept-gdpr 2>&1 | ForEach-Object { "$_" }
     } elseif (Get-Command npx -ErrorAction SilentlyContinue) {
@@ -58,6 +59,9 @@ function Run($a) {
     } else {
         Write-Output "no speedtest CLI found (install Ookla 'speedtest', have npx, or 'pip install speedtest-cli') - skipping"
     }
+    if ($LASTEXITCODE -ne 0) {
+        Write-Output ("(speedtest CLI failed - exit code " + $LASTEXITCODE + "; numbers above may be missing)")
+    }
 
     # 1. Synthetic downloader benchmark (offline, deterministic)
     Run @("scripts/bench_downloader.py", "--segments", "64", "--workers", "1,2,4,8,16", "--runs", "3")
@@ -101,6 +105,7 @@ function Run($a) {
 
     Write-Output ""
     Write-Output ("report saved: " + $out)
-} | Tee-Object -Variable report
-# utf8 (not Tee-Object's utf16) so reports diff and grep cleanly across machines
-$report | Out-File -FilePath $out -Encoding utf8
+} | Tee-Object -FilePath $out
+# progressive tee keeps a partial report if the run dies; rewrite as utf8 at the end
+# (Tee-Object only writes utf16) so reports diff and grep cleanly across machines
+(Get-Content $out) | Out-File -FilePath $out -Encoding utf8