Remove iron integration trait scope restriction

[sehnryr]

Remove private[iron] scope on ValidatorForPredicate, PrimitiveValidatorForPredicate and LowPriorityValidatorForPredicate traits to match with refined integration's.

Then, the documentation for iron's integration won't be misleading:

tapir/doc/endpoint/integrations.md

Line 65 in 16cd9d5

Similarly to `tapir-refined`, you can find the predicate logic in `integrations/iron/src/main/scala/sttp/iron/codec/iron/TapirCodecIron.scala` and provide your own given `ValidatorForPredicate[T, P]` in scope using `ValidatorForPredicate.fromPrimitiveValidator`

In the meantime, I use this workaround:
src/main/scala/sttp/tapir/codec/iron/expose/package.scala

package sttp.tapir.codec.iron.expose

export sttp.tapir.codec.iron.PrimitiveValidatorForPredicate
export sttp.tapir.codec.iron.ValidatorForPredicate

[ahoy-jon]

@sehnryr thank you for the pull request! Straight to the source!

Just to make sure, can you add a test in https://github.com/softwaremill/tapir/blob/master/integrations/iron/src/test/scala-3/sttp/iron/codec/iron/TapirCodecIronTestScala3.scala ?

To check you can use custom constraint in Tapir?

[adamw]

Yeah it would be great to have a test :) Are you planning on adding one, or is this PR ready?

[sehnryr]

I don't know how to write such test, but I can look into it.

[adamw]

Thanks!