Update @github/copilot to 1.0.44-3 (#1239)

* Update @github/copilot to 1.0.44-3

- Updated nodejs and test harness dependencies
- Re-ran code generators
- Formatted generated code

* Align ModelBilling.multiplier optional across SDK public surfaces

The regenerated wire types now treat `ModelBilling.multiplier` as optional,
matching the upstream schema relaxation. Update the hand-coded public surface
mirrors so each language's stable API can represent an absent multiplier
instead of silently coercing to zero (Go/.NET) or raising at decode time
(Python).

- nodejs/src/types.ts: `multiplier?: number`
- go/types.go: `*float64` with `omitempty`
- dotnet/src/Types.cs: `double?`
- python/copilot/client.py: `float | None = None`; from_dict no longer
  raises on absence; to_dict skips serializing None

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Dmytro Struk <13853051+dmytrostruk@users.noreply.github.com>

Author: github-actions[bot]

dotnet/src/Generated/Rpc.cs

@@ -2867,7 +2867,7 @@ public class ModelBilling
     /// Billing cost multiplier relative to the base model rate.
     /// </summary>
     [JsonPropertyName("multiplier")]
-    public double Multiplier { get; set; }
+    public double? Multiplier { get; set; }
 }
 
 /// <summary>