fix(rsc): reset stateful directive regexes

[james-elicx]

Extracted from #1246.

Global and sticky directive regexes retain lastIndex, so later functions or repeated transforms can miss matching directives.

This resets regex state around each match. Tests cover both g and y regexes, multiple functions, repeated transforms, and the final lastIndex.

[hi-ogawa]

Do you have a use case for y? The g case works without resetting.

The fix seems correct and don't mind including it but I'm not sure if when lib provides regex config/option like this, it's always lib side responsibility to normalize in general.