Add cocotb testbench for validating generated bus decoder RTL across APB3, APB4, and AXI4-Lite interfaces (#9)

* Initial plan

* Add cocotb test infrastructure and testbenches for APB3, APB4, and AXI4-Lite

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Add integration tests, examples, and documentation for cocotb testbenches

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Address code review feedback: use relative imports and update installation docs

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Add implementation summary document

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Merge cocotb dependencies into test group

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

* Add optional cocotb simulation workflow with Icarus Verilog

Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: arnavsacheti <36746504+arnavsacheti@users.noreply.github.com>

tests/cocotb/README.md

@@ -0,0 +1,53 @@
+# Cocotb Integration Tests
+
+This directory contains cocotb-based integration tests that verify the functionality
+of generated bus decoder RTL for different CPU interfaces.
+
+## Overview
+
+These tests:
+1. Generate SystemVerilog decoder modules from SystemRDL specifications
+2. Simulate the generated RTL using cocotb
+3. Verify read/write operations work correctly for different bus protocols
+
+## Supported CPU Interfaces
+
+- APB3 (AMBA APB3)
+- APB4 (AMBA APB4 with strobe support)
+- AXI4-Lite (AMBA AXI4-Lite)
+
+## Running the Tests
+
+### Install Dependencies
+
+```bash
+# Using uv (recommended)
+uv sync --group test
+
+# Or using pip
+pip install -e .[test]
+```
+
+### Run All Cocotb Tests
+
+```bash
+pytest tests/cocotb/testbenches/
+```
+
+### Run Specific Interface Tests
+
+```bash
+# Test APB4 interface
+pytest tests/cocotb/testbenches/test_apb4_decoder.py
+
+# Test APB3 interface
+pytest tests/cocotb/testbenches/test_apb3_decoder.py
+
+# Test AXI4-Lite interface
+pytest tests/cocotb/testbenches/test_axi4lite_decoder.py
+```
+
+## Test Structure
+
+- `common/`: Shared utilities and base classes for cocotb tests
+- `testbenches/`: Individual testbenches for each CPU interface