async: remove tag_invoke calls

P2300R9 removed usage of tag_invoke.  stdexec still has it
but in order to be forward compliant with the C++26 standard
we should modernize the code and remove its usage.  This also
has the benefit of simplifying most sender/receiver implementations.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ib0a1d0a82485c8d247a18daa020d0bba2249e95c
diff --git a/src/async/mutex.cpp b/src/async/mutex.cpp
index 44694c6..19e5d3c 100644
--- a/src/async/mutex.cpp
+++ b/src/async/mutex.cpp
@@ -34,7 +34,7 @@
 namespace mutex_ns
 {
 
-void mutex_completion::arm() noexcept
+void mutex_completion::start() noexcept
 {
     std::unique_lock l{mutexInstance.lock};