refactor: refactor tests to replace RIBP references with APB4 equivalents

- Updated test files to change instances of ribp_if to apb4_if in various test cases, ensuring consistency with the new APB4 interface.
- Modified assertions and checks in tests to reflect the new APB4 naming conventions, including changes in expected output and input files.
- Adjusted the test descriptions to accurately represent the APB4 functionality being tested, particularly in timer, UART, and GPIO tests.
- Ensured that all relevant paths and file names in the tests are updated to point to the new APB4 implementations, maintaining the integrity of the test suite.

docs/axi4-stream.md

@@ -1,9 +1,9 @@
 # AXI4-Stream Peripheral Data Paths
 
 The Mini SoC uses 32-bit AXI4-Stream links for high-rate peripheral data that
-does not need an address on every word. RIBP remains the register configuration
+does not need an address on every word. APB4 remains the register configuration
 plane. The active stream endpoints are DMA to I2S TX, I2S RX to DMA, and DVP RX
-to DMA. UART, I2C, and WS2812 retain their existing RIBP FIFO data registers.
+to DMA. UART, I2C, and WS2812 retain their existing APB4 FIFO data registers.
 
 ## Interface Contract