Add Gray counter implementation and testbench

Introduces a synchronous Gray counter with configurable width, reset, enable, and look-ahead functionality. Implements binary-to-Gray and Gray-to-binary conversion functions. Includes a testbench for simulation and validation of the counter's behavior.

tests/GrayCounter_tb.vhd

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+
+library ieee;
+use ieee.std_logic_1164.all;
+use ieee.numeric_std.all;
+
+entity GrayCounter_tb is
+end;
+
+architecture bench of GrayCounter_tb is
+  -- Clock period
+  constant clk_period : time := 10 ns;
+  -- Generics
+  constant G_Width : integer := 6;
+  constant G_InitialValue : integer := 0;
+  constant G_ResetValue : integer := 0;
+  constant G_CountingDirection : string := "UP";
+  constant G_LookAhead : integer := 1;
+  -- Ports
+  signal I_CLK : std_logic := '0';
+  signal I_CE : std_logic := '1';
+  signal I_RST : std_logic := '0';
+  signal I_CountEnable : std_logic := '1';
+  signal O_Value : std_logic_vector(G_Width - 1 downto 0);
+  signal O_LookAheadValue : std_logic_vector(G_Width - 1 downto 0);
+begin
+
+  GrayCounter_inst : entity work.GrayCounter
+  generic map (
+    G_Width => G_Width,
+    G_InitialValue => G_InitialValue,
+    G_ResetValue => G_ResetValue,
+    G_CountingDirection => G_CountingDirection,
+    G_LookAhead => G_LookAhead
+  )
+  port map (
+    I_CLK => I_CLK,
+    I_CE => I_CE,
+    I_RST => I_RST,
+    I_CountEnable => I_CountEnable,
+    O_Value => O_Value,
+    O_LAValue => O_LookAheadValue
+  );
+
+  I_CLK <= not I_CLK after clk_period/2;
+
+end;