MAINT: increase max line length from 79 to 88

There are of course pros and cons, and PEP 8 still recommends 79. However,
lots of tools and recommendations have increased max line length:
- black and ruff have bumped the limit to 88,
- the Linux kernel coding style eventualy bumped the recommended limit from
  80 to 100 characters.

Also, the current codebase contains > 1880 lines wider than 79, against
around 500 lines wider than 88.

Author: DimitriPapadopoulos

tools/lint_diff.ini

@@ -1,5 +1,5 @@
 [pycodestyle]
-max_line_length = 79
+max_line_length = 88
 statistics = True
 ignore = E121,E122,E123,E125,E126,E127,E128,E226,E241,E251,E265,E266,E302,E402,E704,E712,E721,E731,E741,W291,W293,W391,W503,W504
 exclude = numpy/__config__.py,numpy/typing/tests/data,.spin/cmds.py