gh-151464: exclude '<>' token from tokenize output

[skirpichev]

Was:

$ echo '1 <> 2' | python -m tokenize
1,0-1,1:            NUMBER         '1'
1,2-1,4:            OP             '<>'
1,5-1,6:            NUMBER         '2'
1,6-1,7:            NEWLINE        '\n'
2,0-2,0:            ENDMARKER      ''

Now (regardless on __future__.barry_as_FLUFL import):

$ echo '1 <> 2' | ./python -m tokenize
1,0-1,1:            NUMBER         '1'
1,2-1,3:            OP             '<'
1,3-1,4:            OP             '>'
1,5-1,6:            NUMBER         '2'
1,6-1,7:            NEWLINE        '\n'
2,0-2,0:            ENDMARKER      ''

in accordance with the Grammar:
https://docs.python.org/3.14/reference/lexical_analysis.html#operators-and-delimiters

Also adds a custom error message for <> ("not equal" in Pascal and Python 2).

• Issue: Tokenizer produces token '<>', missing in the language grammar (regardless on __future__.barry_as_FLUFL settings) #151464