fix(lib): a malformed select in a resreq fails the parse instead of being dropped (bug-1887)

The primary_resreq action ignored parse_resreq_primary()'s result, so a
primary whose select (or rusage) clause failed to parse was accepted
without that clause: select[type==] or select[mem>] matched every host.
A malformed clause now fails the whole resreq, and parse_resreq() returns
the clause's own message.

A select naming an unregistered resource is still dropped, not an
error: parse_select() reports it as -ENOENT (new select_context_t
.unknown_resource) and the action lets it pass, because jobs rely on it
-- the scheduler's own "type == any" default among them when no "type"
resource is registered (making it fatal failed 36 scheduler suites).

Test: test_resreq_primary_select_error_fails_parse RED before (all
accepted), GREEN after.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/lib/xce_select.peg

@@ -48,6 +48,7 @@
                 snprintf(auxil->errmsg, sizeof(auxil->errmsg),
                     "unknown resource '%s'", name);
             }
+            auxil->unknown_resource = 1;
             auxil->has_error = 1;
             return NULL;
         }