taurus v0.8.0

Performance — parse algorithm over struct size

This release closes the algorithmic parse gap with pugixml via two
targeted hot-path improvements. Element struct size (80 bytes vs
pugixml's 44) remains unchanged — measured analysis shows struct size
is a secondary cache effect, not the dominant cost.

Route predefined entities through the fast parser

The parse-path gate previously fell back to the slow legacy parser
for ANY input containing &, even when only predefined XML entities
(&, <, >, ", ') or numeric character
references (A, B) were present. Since most real-world XML
uses & for escaping, this gate forced the slow path on the
majority of inputs.

Fix: removed the entity gate. The fast path (direct_parse +
flat_promote) now handles predefined entities via lazy expansion:

• direct_parse and flat_promote detect & in attr values, set
  has_entities=1, leave attr->value=NULL so the accessor expands
  via taurus_decode_entities_view on first read.
• taurus_text_get_content checks for & in borrowed content and
  expands before materializing.
• The serializer expands entity-containing attrs before re-escaping.
• taurus_element_get_text_content (XPath string()) routes through
  taurus_text_get_content.

The DOCTYPE internal-subset gate is retained — custom DTD entities
still require the legacy parser.

memchr for attr/comment/CDATA/PI scans in direct_parse

Replaced sequential per-byte scans with libc memchr (SIMD-vectorized,
16-32 bytes/iteration):

• Attribute value closing quote
• Comment body terminator --> (memchr for -, verify candidate)
• CDATA body terminator ]]> (memchr for ], verify candidate)
• PI data terminator ?

Big win for long attribute values (URLs), large comments/CDATA
sections. On a 200KB attr-heavy input: 0.6ms/parse (~333 MB/s),
competitive with pugixml.

Text scanning already used memchr (for <). Name scanning stays
LUT-based — SIMD name scan was tried in TODO 144 and found slower
for typical 5-20 char names (vector setup cost not amortized).

Fixes

• Remove duplicate unreachable return in fp_is_name_char
  (flat_parser.c).
• Remove dead taurus_input_has_entities / taurus_input_has_namespaces
  functions after entity-gate removal.
• Fix two nested-comment warnings in taurus.c.