State the bare-CR line rule in C-220 and C-225

[O6lvl4]

almide/almide#2813 (reported by atzurody): the incumbent wasm leg stripped a trailing bare \r from the last line of string.lines / fs.read_lines / fs.fold_lines — "abc\r" read as ["abc"] where native (str::lines) and the structural leg read ["abc\r"].

The ledger text invited it: C-220 and C-225 said "one trailing \r stripped per line", which is exactly the incumbent's behaviour on an unterminated last line. And the reference evaluator carried the same rule — both string.lines (ref/src/stdlib.rs) and the fs splitter split_lines (ref/src/stdlib_ext.rs) popped a \r from the final unterminated line.

• ref: the final unterminated line keeps a trailing \r; a \r is removed only together with the \n it precedes.
• C-220 / C-225: the statement now says "the \r of a \r\n terminator stripped with it and a bare \r kept as line content (a \r ending the input/file stays on the last line)".
• Fixture spec/wasm_cross/line_endings_bare_cr.almd (evidence for both): CR at the end, doubled at the end, ending the last of two lines, mid-line, before a CRLF, and alone — each line printed with its CRs spelled out, over string.lines, fs.read_lines, fs.fold_lines (String / Int / fallible) and fs.for_each_line.

Local: conformance.py --legs cross,ref over the new fixture plus string_lines.almd / fs_read_lines.almd against the fixed almide build: 3/3 cross, 3/3 ref (judged, no abstain). All pre-commit gates green.

The implementation PR (almide) follows after this merges and the pin advances.