String literal escape sequences are not decoded #10

From the Codex whole-repo review on #5 (review comment).

Location: imp-load.mts:122 on main (6813323)

[P2] Decode escape sequences when constructing string values

For strings containing escapes, this handler only removes the surrounding quotes and retains the escape characters literally. Thus "a\nb" contains a backslash and n rather than a newline, and an escaped quote retains its backslash. This contradicts the documented string syntax and also breaks serialization: impShow uses JSON.stringify, so loading and showing a string repeatedly adds more backslashes. Decode the supported escapes before constructing the string value so printed strings can be read back unchanged.

Checked 2026-10-29: still present on main; not touched by open PRs #3, #4 or #7.