Unconditional ticks/nanoseconds to timespec conversions via a common
helper routine can be costly on low end hardware, putting some useless
pressure on the I-cache when the operation just substitutes an input
constant by another.

Typically, most often the caller passes an infinite wait specification
to blocking Alchemy services, which is translated to NULL for the
copperplate API to start an unbounded wait, so going through a
conversion call to map TM_INFINITE to NULL is pure overhead. In that
case, we would be better off doing the substitution directly from the
calling context.

To thos end, this patch introduces a *_timed() call form for each
blocking Alchemy service, which receives a timespec directly. All
existing relative and absolute call forms of blocking services now
convert the timeout value inline when possible, before branching to
the *_timed() call.