pub const CANONICAL_TS_GLOB: &str = "'[0-9][0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9]T[0-9][0-9]:[0-9][0-9]:[0-9][0-9].[0-9][0-9][0-9][0-9][0-9][0-9]Z'";Expand description
GLOB pattern matching exactly the canonical form.
Used in CHECK constraints. GLOB anchors at both ends and supports
character classes, so this is a complete shape test — no separate
length() term is needed.