rpn: use token-based = detection in handleStandardAssign

Replace fragile strings.Contains checks with proper tokenization.
The old code matched '=' via substring search with hacky guards for
'==' and '!=', which could misparse inputs like 'a == b = 5'.

Now Tokenize(input) splits on whitespace first, so '=' is only
detected as a standalone token — '==' and '!=' are naturally distinct
tokens and can never trigger a false positive.

Also adds regression tests confirming == and != are not treated as
assignments.

0 files changed, 0 insertions, 0 deletions