cache compiled eval tags in safeEval feature for better hx-live perf

[MichaelWest22]

Description

Found that hx-csp creates temporary script tags via its safeEval feature but when using things like hx-live this means it re-creates the same eval script each dom update. We can easily cache the functions and reuse them so they do not need to be be re-created every time.

Corresponding issue:

Testing

Tested this manually in a test project to confirm faster performance during events. It went from ~2ms to fire a small batch of expressions down to ~1.2ms. before safe-eval was a bit slower by design than normal eval but now it is just a little bit faster but the perf difference is hard to notice comparing the two.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded

[1cg]

Thank you!