Revised ProxyChannel interfaces (#400)

* Renamed `ProxyChannel` -> `BaseProxyChannel` and `SimpleProxyChannel`
-> `ProxyChannel`. It makes the interface more consistent by defining
channels to be associated with a certain src/dst memory region:
`ProxyChannel` as "sema + src/dst + fifo" and `SmChannel` as "sema +
src/dst". BaseProxyChannel is not associated with any memory regions, as
"sema + fifo".
* `ProxyChannelDeviceHandle` now inherits from
`BaseProxyChannelDeviceHandle`, instead of having one as a member.

docs/getting-started/tutorials/python-api.md

@@ -47,7 +47,7 @@ We provide some Python utils to help you launch kernel via python. Here is a exa
 ```python
 from mscclpp.utils import KernelBuilder, pack
 
-def launch_kernel(my_rank: int, nranks: int, simple_channels: List[SimpleProxyChannel], memory: cp.ndarray):
+def launch_kernel(my_rank: int, nranks: int, simple_channels: List[ProxyChannel], memory: cp.ndarray):
     file_dir = os.path.dirname(os.path.abspath(__file__))
     kernel = KernelBuilder(file="test.cu", kernel_name="test", file_dir=file_dir).get_compiled_kernel()
     params = b""
@@ -77,7 +77,7 @@ The test kernel is defined in `test.cu` as follows:
 
 // be careful about using channels[my_rank] as it is inavlie and it is there just for simplicity of indexing
 extern "C" __global__ void __launch_bounds__(1024, 1)
-    simple_proxy_channel(mscclpp::SimpleProxyChannelDeviceHandle* channels, int my_rank, int nranks,
+    proxy_channel(mscclpp::ProxyChannelDeviceHandle* channels, int my_rank, int nranks,
                          int num_elements) {
     int tid = threadIdx.x;
     int nthreads = blockDim.x;