The whole-buffer ISO-2022-JP, GB18030, and EUC-TW decoders index the input
ArraySlice directly instead of materializing an Array first (one avoidable
O(n) allocation per decode each); declaredEncoding's subsequence scan uses
elementsEqual instead of allocating an Array per candidate offset. Document
the two analysis-flagged bounds: entity expansion is doubly bounded (the
character budget caps output; the visiting set caps recursion depth at the
number of declared entities), and the RELAX NG derivative engine carries no
memoization by design (the simplifying constructors keep real grammars
small; adversarial nested-choice grammars can grow the residual, so treat
untrusted schemas accordingly). Behavior unchanged, all suites green.
Closes#118
Extend the GBK two-byte subset to full GB18030: a lead byte followed by
a digit opens a four-byte form whose pointer is mapped through the WHATWG
index-gb18030-ranges linear ranges, reaching the supplementary planes.
The 207 ranges are vendored verbatim. Wired into the whole-buffer and
streaming decoders and the encoding-name table (gb18030/gb-18030).
Closes#102
