Fix AOT compatibility in streaming mode

[Copilot]

Encoding.GetEncoding(charset) is not AOT-compatible due to runtime encoding provider lookup. Streaming mode now uses static Encoding.UTF8 to maintain AOT compatibility.

Changes

• Replace dynamic Encoding.GetEncoding(charset) with Encoding.UTF8 in RequestExecutor.InvokeStreamingRequest
• Update byte encoding to use Encoding.UTF8.GetBytes() consistently

-var encoding = responseMessage.Content.Headers.ContentType?.CharSet is { } charset
-    ? System.Text.Encoding.GetEncoding(charset)
-    : System.Text.Encoding.UTF8;
-using var reader = new StreamReader(stream, encoding);
+// Use UTF-8 encoding for AOT compatibility (Encoding.GetEncoding is not AOT-safe)
+using var reader = new StreamReader(stream, Encoding.UTF8);

Trade-off: Responses using non-UTF-8 encodings may not display correctly in streaming mode. This matches ResponseMapper behavior which also assumes UTF-8.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• httpbin.org
  • Triggering command: /home/REDACTED/work/dotnet-httpie/dotnet-httpie/tests/HTTPie.IntegrationTest/bin/Debug/net10.0/HTTPie.IntegrationTest /home/REDACTED/work/dotnet-httpie/dotnet-httpie/tests/HTTPie.IntegrationTest/bin/Debug/net10.0/HTTPie.IntegrationTest --internal-msbuild-node /tmp/51ac26f264ff48b284bf0405fdb09839 (dns block)
• reservation.weihanli.xyz
  • Triggering command: /home/REDACTED/work/dotnet-httpie/dotnet-httpie/tests/HTTPie.IntegrationTest/bin/Debug/net10.0/HTTPie.IntegrationTest /home/REDACTED/work/dotnet-httpie/dotnet-httpie/tests/HTTPie.IntegrationTest/bin/Debug/net10.0/HTTPie.IntegrationTest --internal-msbuild-node /tmp/51ac26f264ff48b284bf0405fdb09839 (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)