taurus v0.9.0

direct_parse handles DTD entities — path to deleting legacy parser

The legacy parser (parser_new.c, 1955 lines) existed primarily to
handle DTD internal subsets with custom entity declarations. This
release makes direct_parse DTD-aware, enabling deletion of the
legacy parser in a future release.

Changes

• DOCTYPE extraction: when direct_parse encounters
  <!DOCTYPE name [subset]>, it extracts the internal subset and
  parses it via taurus_dtd_parse_internal_subset (reusing the
  existing DTD parser). A DOCTYPE node is created so
  taurus_document_internal_subset exposes the name.

• Entity expansion: when a DTD is present and text/attr content
  contains &, entities are eagerly expanded via
  taurus_decode_entities_view_with_dtd. Predefined entities
  (& etc.) still use the lazy expansion path when no DTD.

• Parse-path gate: the DTD internal-subset gate in taurus_parse
  is removed. direct_parse now handles DTD inputs directly —
  no more forced legacy-parser fallback for <!DOCTYPE> inputs.

• Serializer: serialize_text_internal now routes through
  taurus_text_get_content so borrowed text nodes with entities
  are materialized + expanded before output.

Verified

<!DOCTYPE root [<!ENTITY foo "Hello">]><root>&foo;</root> parses
via direct_parse with text content "Hello" (was "&foo;"
before this change).

Next steps (future releases)

Once confidence builds that direct_parse handles all real-world
DTD inputs:

• Remove flat_parse fallback from taurus_parse.
• Delete the legacy parser (parser_new.c, ~1955 lines).
• Delete flat_parser.c + flat_promote.c (~1245 lines).
• Total: ~3200 lines of parser code removed.