This breaks the API since some functions didn't take a VRT_CTX until now.

Closes #2860

returns version related strings.

Get rid of global, but pretty useles variable VCS_version.

Closes: #2936

And sync the documentation with the current behavior, part of which used
to be implicit.

This is how std.ip is documented, so VSS_ResolveOne doesn't work there.
It might not be the only migration to VSS_ResolveOne that requires
attention.

Speaking of attention, VSA_Malloc may require some.

It can now be shared by established callback-based resolvers and the new
VSS_ResolveOne. This also changes the semantics of VSS_ResolveOne in the
sense that the port is now a default port, overriden by the address if
it contains one.

Also make it clear that VTCP was already relying on a VSS function that
didn't and still doesn't allow a null errp argument, while conversely
all VTCP_open call sites provide a valid errp argument.

At this point the workspace already overflowed so there's no point
making further progress to fail on the next workspace operation.

Incidentally, we are failing for an IP conversion, not an integer.

We do not hold a reference, the magic can be unstable.

The name implies that this is not for production usage.

There are a surprising number of subtle corner cases here, and I
think I have handled them all correctly, but caveat emptor...

With recent changes in the VCL state and temperature handling this test
case lost its relevance and started testing a no-op operation. And since
it wasn't apparently obvious what it was trying to check between two
possible interpretations it now tests both and better verifies it.

Reported by fgs.

When I initially wrote this test case it used to trigger a panic in the
then young VCL labeling.

If an absolute path is provided as n_arg with a length of exactly
PATH_MAX-1 then the combination of strcpy and strcat for the trailing
slash '/' overflows dn by one byte, writing its new null-terminating
character '\0' right after dn's upper bound.

By using a fixed-length VSB we can simply ensure that we stay within
bounds at a reasonable cost. Guarding VSB operations should silence
Flexelint as a nice side effect.

VIN_n_Arg is not exposed outside of the source tree, and both callers
today provide a valid dir argument, so we can now make it part of the
contract with an assertion, simplifying the strdup error handling.