Merge branch 'develop-examples-fpga-helloworld'. Close #657.

**Description**

We need an example that demonstrates how to work with FPGAs using
Copilot. This will help users start with `copilot-bluespec`, and also
help validate our work.

**Type**

- Feature: New example.

**Additional context**

None.

**Requester**

- Ivan Perez.

**Method to check presence of bug**

**Expected result**

The `copilot` package includes an example that shows how to use
`copilot-bluespec`.

**Solution implemented**

Create README under `copilot/examples/fpga`, in a folder for the
specific example.

Add any necessary auxiliary files.

**Further notes**

None.

Author: ivanperez-keera

copilot/CHANGELOG

@@ -1,3 +1,6 @@
+2025-08-21
+        * Add hello world example for FPGA. (#657)
+
 2025-07-07
         * Version bump (4.5). (#642)
 

copilot/examples/fpga/HelloWorld/HelloWorld.hs

@@ -0,0 +1,19 @@
+module Main where
+
+import Language.Copilot
+import Copilot.Compile.Bluespec
+
+-- Define switches input
+sw :: Stream Word8
+sw = extern "sw" Nothing
+
+-- Define LEDS output
+leds :: Stream Word8
+leds = sw
+
+spec = do
+  trigger "leds" true [arg leds]
+
+main = do
+  spec' <- reify spec
+  compile "HelloWorld" spec'