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
Add EUC-TW for the whole-buffer and streaming decoders: ASCII, a two-byte
plane-1 pair, and a 0x8E four-byte plane selector plus a pair. CNS planes 1
and 2, which carry essentially all real-world EUC-TW text, are vendored from
the ICU euc-tw-2014 mapping (private-use fallbacks dropped); planes 3-15 are a
documented follow-up. Tested for plane 1 (two-byte and four-byte forms), plane
2, and streaming. The streaming method moved to its own file to stay under the
type-body cap.
Closes#108
