Two issues were fixed in the split regex:
1. Special characters before `.` were ignored:
The old regex only split on `.` when directly preceded by a word
character (\w), causing splits to be missed when `.` was preceded
by special characters like whitespace, / or $.
Result before: `foo /.bar.one` => `['foo /.bar', 'one']`
Result after: `foo /.bar.one` => `['foo /', 'bar', 'one']`
2. Brackets mid-word were incorrectly split:
The old regex split before any `[`, causing keys like `con[0]cat` to be
split incorrectly.
Resulti before: `con[0]cat` => `['con', '[0]cat']`
Now splits before `[` only when it's a standalone array index — meaning
`]` is followed by `.`, another `[`, or end of string.
Result after: `con[0]cat` => `['con', '[0]', 'cat']`