fix CI compilation error by replacing let_value

stdexec::just() | stdexec::let_value(f) where f takes no arguments is
semantically identical to calling f() directly, since just() sends no
values and let_value simply forwards them to f.

Replace the pattern with the direct call to avoid the let_value
constexpr completion-signature computation path, which triggers a
compile error in stdexec's __typeinfo.hpp due to pointer comparison of
inline constexpr globals in a constant expression context.

In sensor_manager.cpp an immediately-invoked lambda expression is used.
In handler_test.cpp the lambda is stored in a named variable before
invocation to preserve the closure lifetime across coroutine suspension
points, matching the original behavior where let_value held the closure
in its operation state.

No behavior change.

Change-Id: I3c6b6a432d3a5c594ea7a99b5c9e338898e3893a
Signed-off-by: Vishnunithyasoundhar S <vishnunithyasoundhar.s@intel.com>