Improve compile error message for values that cannot be exported

[lbialy]

Currently for types that do not have an instance of Encoder[A] compile error for exports function looks like this:

Compiling project (Scala 3.3.1, JVM (11))
[error] ./Main.scala:113:22
[error] Encoder[os.Path] is missing
[error]     kubeconfigPath = os.pwd / "kubeconfig.conf"
[error]                      ^^^^^^^^^^^^^^^^^^^^^^^^^^
Error compiling project (Scala 3.3.1, JVM (11))
Compilation failed

for code:

  yield exports(
    leaderIp = leaderIp,
    kubeconfigPath = os.pwd / "kubeconfig.conf"
  )

We should improve the error message here and explain what's going on. Maybe even offer public Encoder access with contravariant combinator?

[lbialy]

This happens in Exports.scala:24-56, applyDynamicNamedImpl macro method scope. Precise location Exports.scala:39 but it gets called on line 44.

[lbialy]

The workaround is to convert your type here to something that has an obvious Encoder instance like any numeric type, Strings and spray.json JSON AST values.