pytest-selfie initial acceptance tests

[nedtwigg]

Basic acceptance tests

fun comment_removal(): #selfieonce
  expectSelfie("nothing happens")
  pass

fun inline():
  expectSelfie("A").toBe_TODO()

fun disk():
  expectSelfie("A").toMatchDisk_TODO()

• Loosely based on https://github.com/diffplug/selfie-python-wip/tree/main/jvm/selfie-runner-junit5

https://github.com/diffplug/selfie-python-wip/blob/f8f51a4d2b1ac22a6df3f61353454b48b38e1c06/jvm/selfie-runner-junit5/src/main/kotlin/com/diffplug/selfie/junit5/SelfieTestExecutionListener.kt#L26-L88

https://github.com/diffplug/selfie-python-wip/blob/f8f51a4d2b1ac22a6df3f61353454b48b38e1c06/jvm/selfie-runner-junit5/src/main/kotlin/com/diffplug/selfie/junit5/SnapshotSystemJUnit5.kt#L61-L306

[nedtwigg]

• start with expectSelfie(actual: str)
• backed by SnapshotSystem
• pytest plugin model is similar to https://github.com/diffplug/selfie/blob/main/jvm/selfie-runner-kotest/src/commonMain/kotlin/com/diffplug/selfie/kotest/SelfieExtension.kt