Add Blink() extension method for StringBuilder

[codegen-sh]

This PR adds a new Blink() extension method to the AnsiExtensions class that applies the ANSI BLINK attribute to StringBuilder instances.

Changes Made

• Added Blink() extension method in src/Ansi/AnsiExtensions.cs

  • Uses the existing Mode.Blink enum value (ANSI code 5)
  • Follows the same pattern as other formatting methods
  • Simple one-liner: b.SetMode( Mode.Blink )

• Updated console test in src/Ansi.ConsoleTest/Program.cs

  • Added demonstration of the new Blink() method
  • Shows " BLINK!" text with blinking effect

Usage

var sb = new StringBuilder()
    .Append("Normal text ")
    .Blink()
    .Append("This text will blink!")
    .SetMode(Mode.Reset);

The method integrates seamlessly with the existing fluent API and follows all established patterns in the codebase.

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