Fix unnamed placeholders extraction

[sdnunca]

The unnamed placeholder logic skips positional placeholders, which it determines as:
% followed by anything followed by $.

This causes strings such as:

Test %s with $ after

to be interpreted as having a %s with $ positional placeholder, returning [].

This PR makes the logic to determine positional placeholders more specific:
% followed by a number followed by $.

[aduth]

Thanks for the patch! This change makes sense to me, though I'd be curious for @USERSATOSHI's feedback as well, since he authored the typings.

[USERSATOSHI]

Oh, nice catch. I have tested the patch and it works great. So Looks good to me.

cc: @sdnunca @aduth

[aduth]

Thanks @USERSATOSHI for the review, and thanks again @sdnunca for the fix. I'll get this published shortly.

[aduth]

This is now published in @tannin/sprintf@1.3.3 🚀