GeezerVison

split_args parses the ExecutableArguments and WindowedExecutableArguments values of PEP 514 registrations. It only handles quotes that wrap a whole argument. When a quote starts or ends inside an argument, the parser keeps a stray quote (-W"ignore" becomes -W"ignore) or drops text ("a b"c becomes a b). It also collapses \\ outside quotes and turns doubled spaces into empty arguments.

This change replaces the parser with a character-by-character implementation of the C runtime rules:

• Whitespace (space or tab) outside quotes separates arguments.
• 2n backslashes followed by a quote produce n backslashes and toggle quoting.
• 2n+1 backslashes followed by a quote produce n backslashes and a literal quote.
• A doubled quote inside a quoted section produces a literal quote.
• Other backslashes are kept as is.

The new test_split_args cases include the examples from Parsing C command-line arguments. The existing quote_args round-trip cases still pass.

Fixes #438