feat(resreq-maxtasks-wiring): add task-count derivation helper

Adds apply_job_task_count() to overwrite a standalone primary resreq's
minTasks/maxTasks with a job's real requested task count, no-op for
COMPOUND/ALTER nested primaries, with a defensive min>max clamp.
Closes the gap that lets scheduler-allocation's multi-host allocator
ever be reached (bug-1770). Wiring at live ingest call sites follows
in subsequent tasks.

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

src/lib/meson.build

@@ -160,6 +160,7 @@ libxce_test_src = ['testsuite/test.c',
                    'testsuite/test_xvec.c',
                    'testsuite/test_resreq.c',
                    'testsuite/test_resreq_fingerprint.c',
+                   'testsuite/test_resreq_task_count.c',
                    'testsuite/test_resmgr_fixture.c',
                    'testsuite/test_select.c',
                    'testsuite/test_bitset.c',