Add a resumable XML scanner that reports a token only once its terminator is
fully buffered and otherwise signals need-more (the Expat XML_TOK_PARTIAL
model), and PushParser with feed(_:)/finish() driving a SAXHandler while
retaining only the current incomplete token plus the open-element stack.
events(feeding:) exposes an AsyncThrowingStream of events over any async
sequence of text chunks. Splitting a document at any byte boundary, down to
one character per feed, yields identical events. Collapse the completed
roadmap into the legend summary.
Closes#4Closes#5Closes#6Closes#7Closes#1
