fix(controller,xceadmin): fix zero-slot scheduling block, misleading resval logs, byte-unit display

Three bugs found while diagnosing a live controller log, all in the
worker resource-value path:

1. Every host relying on the documented hosts.yaml auto-detect default
   (no max_slot, meaning "use CPU count") got 0 scheduling slots,
   permanently blocking the scheduler from placing jobs on it. mxj is
   UInt32 on the wire and can't carry the schema's -1 sentinel; mapping.py
   worked around this by leaving it unset, which defaults to 0 -- and 0 is
   never < 0, so apply_join_state()'s auto-detect fallback never fired.
   Fixed by encoding the sentinel as 0xFFFFFFFF, which the controller's
   `int mxj` field reinterprets back to -1 via its existing implicit
   uint32_t->int conversion. No C-side or wire schema change needed for
   this part; the fallback itself was already correct but had zero test
   coverage for a negative mxj, now added.

2. update_resvals()/update_resval_list() logged the failure reason via
   PERROR, which reads process-global errno -- but update_resval()'s
   failure paths return raw negative codes directly and never touch
   errno, so the controller log filled with misleading "update_resval:
   Success" / "update_resval: Resource temporarily unavailable" lines
   instead of the real reason. Fixed to decode the actual rc via
   xce_strerror_r and name the failing resource.

3. maxmem is canonically stored/wired as raw bytes but had no unit
   metadata, so resval/workerlist printed it as a bare number that read
   as garbage (e.g. workerlist's fixed-width columns visually smeared a
   multi-GB byte count across the MaxCPU/MaxMem headers). Added an
   optional `unit` field to the Resource/ResourceVal capnp structs (and
   xce_resource_t/xce_resval_t/resources.yaml) so resval and workerlist
   can render a human-readable value (e.g. "30.90 GB") while the stored
   value stays raw bytes -- display-only, every other resource unaffected.

Regenerated the xceadmin golden fixture (fixtures/full/expected.bin)
twice: once for the mxj sentinel encoding change, once for the new
Resource.unit field growing every resource's wire size by one pointer
slot. Both diffs verified byte-for-byte isolated to exactly the expected
change before regenerating.

Verified: 1095/1095 controller_unit_test (stable across repeated runs),
229/229 xceadmin pytest, clean rebuild of lib/controller/xceadmin/xce_test.
Two related findings logged to .wolf/buglog.json but deliberately not
fixed here (out of scope per discussion): a pre-existing flaky segfault
in the combined controller_unit_test binary, and maxswap/maxtmp being
hardcoded stub values on the worker side.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/lib/resobj.c

@@ -35,6 +35,7 @@ static int resobj_init(meta_obj_t* obj, va_list ap)
 
     dst->name = makeString(src->name);
     dst->desc = makeString(src->desc);
+    dst->unit = makeString(src->unit);
 
 #if 0
     if (src->distributions != NULL) {
@@ -64,6 +65,7 @@ static void resobj_destroy(meta_obj_t* obj)
 
     dereference(r->name);
     dereference(r->desc);
+    dereference(r->unit);
 
     memset(priv, 0x0, sizeof(*priv));