Efficient strategy for st.text(...).filter(str.isidentifier)

[Zac-HD]

As a follow-up to #2693 (comment) and #3134, I'd like to return an efficient strategy for st.text(...).filter(str.isidentifier).

Adapting https://github.com/Zac-HD/hypothesmith/blob/85358991f8498db489569e81ac9dc9049c75773f/src/hypothesmith/syntactic.py#L39-L56 should make this pretty easy, even with the slight complication of incorporating the restrictions of the alphabet= strategy.

We could optionally add similar support for the other str.isX methods, which mostly impose simpler constraints and could be satisfied more efficiently by replacing the self.elements strategy (e.g. str.isspace requires all-whitespace chars), and for some adding the filter on at the end (e.g. str.isupper is satisfied if all cased characters in the string are uppercase and there is at least one cased character).

Note that st.characters().filter(...) will often be considerably simpler; we can compute and cache the allowed characters directly - although often more quickly than by naive iteration, if we're willing to spend some code on it.

[Zac-HD]

Closed in #3725 🎉