libcasper: Neuter false positive -Wuse-after-free warnings from GCC 13

GCC 13 incorrectly thinks a call to free after a failed realloc is a
use after free.

lib/libcasper/services/cap_grp/cap_grp.c: In function 'group_resize':
lib/libcasper/services/cap_grp/cap_grp.c:65:17: error: pointer 'buf' may be used after 'realloc' [-Werror=use-after-free]
65 | free(buf);
| ^~~~~~~~~
lib/libcasper/services/cap_grp/cap_grp.c:63:19: note: call to 'realloc' here
63 | gbuffer = realloc(buf, gbufsize);
| ^~~~~~~~~~~~~~~~~~~~~~

Reviewed by: imp, emaste
Differential Revision: https://reviews.freebsd.org/D42576

Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

libcasper: Move helper libraries from /lib/casper to /lib.

These libraries are linked to directly by applications rather than
opened at runtime via dlopen().

Discussed with: oshogbo
Reviewed by: markj, emaste
Differential Revision: https://reviews.freebsd.org/D39245

libcasper: Create a minimal cap_netdb service

Create a casper service for netdb functions.
Initially only cap_getprotobyname is implemented.

This is needed for capsicumizing sockstat.

Reviewed by: oshogbo, bcr (manpages)
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D24832