Append a new contributor entry for Will Speak with their email address
to the project's AUTHORS file, following the existing formatting
convention used for other contributors.
Extend the compiler's string parser to handle `\U` escapes with 8 hex digits
for codepoints above U+FFFF, replacing the previous TODO comment. The
`readUnicodeEscape` helper now accepts a variable digit count (4 or 8) and
the `readString` function dispatches `\u` with length 4 and `\U` with length 8.
New test cases verify correct encoding of emoji and ancient scripts, plus
error handling for incomplete long escapes and values that fit in 4 digits.
Will Speak