Fix #7: Code readthrough, comments

[leftibot]

Automated fix by @leftibot.

What changed

Fix #7: tokenizer treats \\ before " as escaped terminator
next_token set in_escape = true on every backslash instead of
toggling it. After an even run of backslashes the flag stayed true, so
the following " was consumed as an escaped quote and the tokenizer
ran past the end of the literal. Toggling in_escape makes each
backslash cancel its predecessor, matching what process_string_escapes
already does in the second pass.
Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

Files

 include/cons_expr/cons_expr.hpp |  2 +-
 test/string_escape_tests.cpp    | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

Closes #7

Triggered by @lefticus.