feat(job-array-one-based-index): bounded job-identity and element-selection parser in libxce (task 1.1)

parse_jobsel() parses c-a-ts-seq with an optional [k] or [a-b] under a
fixed grammar and check order (syntax, field widths, array-identity
alignment, element bound, reversed range), saturating digits so an
oversized number cannot wrap; plus is_array_tag(), jobsel_element_id(),
jobsel_strerror() and JOBID_FIELD_MAX_* constants. The selection-cases
conformance table runs in the libxce suite.

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

src/lib/meson.build

@@ -183,6 +183,7 @@ libxce_test_src = ['testsuite/test.c',
                    'testsuite/test_zarray.c',
                    'testsuite/test_config.c',
                    'testsuite/test_idgen.c',
+                   'testsuite/test_jobsel.c',
                    'testsuite/test_delay.c',
                    'testsuite/test_ordq.c',
                    'testsuite/test_preason.c',