cfunction
(scan-number str)
Parse a number from a byte sequence an return that number, either and
integer or a real. The number must be in the same format as numbers in
janet source code. Will return nil on an invalid number.
(scan-number "123") # => 123
(scan-number "f") # => nil
(scan-number 123) # =>
# error: bad slot #0, expected string|symbol|keyword|buffer, got 123
# in scan-number
# in _thunk [repl] (tailcall) on line 1, column 1