test: add unit tests for static helpers in fabrics.c

[martin-belanger]

@igaw - I thought it would be a good idea to add unit tests for the static functions in fabrics.c including traddr_is_hostname().

Adds libnvme/test/test-fabrics.c, which tests the static helper functions in src/nvme/fabrics.c without modifying any production source.

The technique is to define static to nothing and then #include the source file directly. This exposes all translation-unit-local symbols in the test binary. No #ifdef UNIT_TEST guards or visibility changes are needed — the production files are left completely untouched.

Functions covered:
strchomp, hostid_from_hostnqn, __add_bool_argument, __add_hex_argument, _add_int_argument, __add_int_or_minus_one_argument, __add_argument, inet4_pton, inet_pton_with_scope, traddr_is_hostname, unescape_uri

The test is gated on want_fabrics in meson.build, matching the conditional that guards the uriparser test above it.

The traddr_is_hostname tests include the key regression case: scoped IPv6 addresses (e.g. "fe80::1%lo") must not be mis-classified as hostnames. A plain inet_pton() call would fail on the % delimiter and wrongly return true; inet_pton_with_scope() handles it correctly.

[igaw]

Thanks. Let's see how this goes in the long run. I do think having proper unit tests also for such functions is not a bad thing. Though it has the change to get out of hand. But that's tomorrow's problem.