Ichor.Actions implementation for Dextrin.Text.Grammar — turns
the raw capture tree Grammar.Native produces while matching
priv/grammar/dxn.aether into actual Dextrin.Value.t() values.
context is a Dextrin.Registry.t() — text parsing only ever reads
it (to resolve struct schemas and custom tags), never mutates it.
handle_token/3 covers every scalar (numbers via
String.to_integer/Float.parse/Decimal.new/a manual rational
split; strings/chars through the shared escape-decoding in
Dextrin.Text.Escapes so string bodies and char literals never
duplicate escape logic); handle_rule/3 covers every collection and
tag_form (a dispatch table: built-in tag names from DXN.md §1.3
go to a hardcoded handler in dispatch_tag/3, anything else falls
through to a Dextrin.Registry lookup, then to Dextrin.CustomTag
as the last resort).