feat(scheduler-allocation): add resreq fingerprinting for the cache

Adds rusage_hash to xce_primary_resreq_t (computed once by
parse_resreq_primary() via a new hash_rusages() helper, hashing
rusage content rather than raw struct bytes since resname is a
non-interned strdup'd pointer), the xce_resreq_fingerprint_t value
type, and resreq_fp on xce_primary_schedobj_t, populated once at real
job-ingest time in core_build_primary_schedobj().

Task 1.2 (scheduler-allocation spec). Requirement 7.1.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XYdtrEWWZfKRRGED7raEYg

src/lib/meson.build

@@ -159,6 +159,7 @@ libxce_test_src = ['testsuite/test.c',
                    'testsuite/test_limit.c',
                    'testsuite/test_xvec.c',
                    'testsuite/test_resreq.c',
+                   'testsuite/test_resreq_fingerprint.c',
                    'testsuite/test_resmgr_fixture.c',
                    'testsuite/test_select.c',
                    'testsuite/test_bitset.c',