fix: remove utf-8 bom from bfgsoptimizer.cs

- Remove byte order mark (BOM) from beginning of BFGSOptimizer.cs file
- File now starts directly with 'using' directive as expected
- Resolves Issue #94 from code review (MINOR encoding issue)

UTF-8 BOM can cause compatibility issues with some tools and is unnecessary
for C# source files which default to UTF-8 encoding.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ooples

src/Optimizers/BFGSOptimizer.cs

@@ -1,4 +1,4 @@
-using Newtonsoft.Json;
+using Newtonsoft.Json;
 
 namespace AiDotNet.Optimizers;