A block scalar's leading empty lines must not be more indented than its
first non-empty line, so a blank line wider than the content (a 5-space
blank above 2-space content, or 2,3-space blanks above 1-space content) is
malformed. The scanner buffered the leading blanks without comparing their
indentation to the content, folding such input into the value.
The scanner now records the widest leading blank and rejects the scalar
when it exceeds the content indentation, established for both auto-detected
and explicit indicators. Indentation is counted in leading spaces, not
tab-expanded width, so a tab on a blank line ('␣\t') is one space rather
than a jump to the next tab stop, keeping such valid block scalars intact.
Measured against the official YAML test-suite, parse-level conformance
rises from 270/333 (81.1%) to 273/333 (82.0%) with no regression.
A block scalar terminated by a less-indented comment line failed with a
spurious 'unexpected indentation': once the smaller indentation ended the
scalar, the comment's own column was processed as a dedent, and because no
indentation level held that width the dedent raised an error. A comment's
indentation does not participate in block structure, so a comment that ends
a block scalar is now left for the main loop to scan, with the block
scalar's own first content line (which may itself begin with '#') still
treated as content.
Separately, a whitespace-only line indented past a block scalar's content
level lost its surplus spaces because the width was consumed before the
line was recognized as blank; the surplus is now preserved as the line's
content, so an over-indented blank contributes the correct value.
Measured against the official YAML test-suite, parse-level conformance
rises from 240/333 (72.1%) to 243/333 (73.0%) with matching value-level
gains, and no regression.
Blank lines between a block scalar header and its first content line come
before the indent token, so the earlier blank-line capture skipped them.
Buffer leading blanks while the block indentation is still pending and
flush them as empty content once the indent is established, in the shared
indentation path used by both scan loops. Also fix folded bodies to emit
a break for a leading blank rather than folding it into a leading space.
This closes the last block-scalar blank-line edge from #57.
