Add ETS-backed storage backend

[rapind]

Summary

• Adds glimit/ets_store module, an ETS-backed implementation of bucket.Store
• ETS operations are lock-free and concurrent, avoiding the overhead of OTP actor
  messages. Suitable for single-node deployments where low latency matters.
• Adds glimit.ets_store() builder for easy integration
• Includes periodic sweep timer for cleaning up full and idle buckets
• 10 new tests covering all ETS store functionality
• README updated with ETS mode documentation

Usage

let limiter =
  glimit.new()
  |> glimit.per_second(10)
  |> glimit.ets_store()
  |> glimit.identifier(fn(request) { request.ip })
  |> glimit.on_limit_exceeded(fn(_) { "Rate limit reached" })

Test plan

• All 10 new ETS store tests pass
• All 67 existing tests still pass (77 total)

[nootr]

Hi @rapind, thank you very much for these PR's. I'll code review them this weekend.

Would this be an option to use as the default in-memory backend? What do you think?

[rapind]

Would this be an option to use as the default in-memory backend? What do you think?

Yes, 100% it's an upgrade. Same behaviour without the serialization bottleneck. I can rework this PR to replace the default if you like.

[nootr]

@rapind That would be great! I think there would be no use for the current in-memory backend (OTP actor), so it would be awesome if this could completely replace that.

Let me know if I could help, thank you very much for contributing!

[rapind]

All set.

[nootr]

Hi @rapind,

thanks again for your time and effort. This looks great!

I have a couple of questions, but overall this is a great improvement. Also, the pipeline seems to fail due to a formatting error.

[nootr]

@rapind Thank you for helping!