#0: update all-gather tests to remove all_devices test fixture

The all_devices test fixture is unreliable for producing expected chip orderes that are needed for certain CCL operations such as ring all-gathers. Without this change, from machine to machine, the chip order may be incorrect from the order expected by all-gather. To correct the chip, we use fixtures that account for chip ordering.

In particular, 4-chip ring tests that are expected to run on the inner 4-chip ring of the t3000 were updated to use the pcie_mesh_device fixture to ensure that the first 4 chips in the list are those devices in the inner ring.

Additional changes along with the above:
- Removed some redundant `run_all_gather` type test functions to merge into a singla test function
- Added additional n300 all-gather test cases
- Improve error messaging

conftest.py

@@ -248,6 +248,29 @@ def pcie_mesh_device(request, silicon_arch_name, silicon_arch_wormhole_b0, devic
     del mesh_device
 
 
+@pytest.fixture(scope="function")
+def n300_mesh_device(request, silicon_arch_name, silicon_arch_wormhole_b0, device_params):
+    import ttnn
+
+    if ttnn.get_num_devices() < 2:
+        pytest.skip()
+
+    mesh_device = ttnn.open_mesh_device(
+        ttnn.MeshShape(1, 2),
+        dispatch_core_type=get_dispatch_core_type(),
+        **device_params,
+    )
+
+    logger.debug(f"multidevice with {mesh_device.get_num_devices()} devices is created")
+    yield mesh_device
+
+    for device in mesh_device.get_devices():
+        ttnn.DumpDeviceProfiler(device)
+
+    ttnn.close_mesh_device(mesh_device)
+    del mesh_device
+
+
 @pytest.fixture(scope="function")
 def t3k_mesh_device(request, silicon_arch_name, silicon_arch_wormhole_b0, device_params):
     import ttnn