Support regex rules with an end-anchor (`$`)

Consider the following filter:
```adblock
/^https?:\/\/[a-z]{8,15}\.top\/[a-z]{4,}\.json$/$xhr,3p,match-case
```
There are two `$` characters in the filter. The first represents an anchor to the end of a URL, and the second separates the pattern part of the filter from the options.

`adblock-rust` currently treats the first `$` character as the separator, such that the pattern no longer ends with a `/` character. `match-case` is only supported for regex rules, so the rule is ultimately considered invalid.

Start by reproducing the issue with the filter shown in the report and trace how regex rules locate the options separator. Confirm the existing parse result, then verify that the end-anchor remains part of the pattern and that the rule is accepted with its options.

Written by the indexing model from the issue text.