chore: add spoon-test to check that spoon works on any repo

I propose to add a script `spoon-test` as follows:

spoon-test https://github.com/google/guava

It would:

* check that the model can be built without any exception (contract inspired from build.sh)
* check that the pretty-printed code can be compiled with any exception (contract inspired from build.sh)
* check that the pretty-printed code passes all the test (contract inspired from build.sh)
* check all contracts on the model (see #2716)

This is basically a rework or extension of `build.sh`. We may consider a clean Python or Groovy version instead of this Shell monster.

Start by reading build.sh and the contract discussion in #2716, then compare the proposed spoon-test checks for model building, pretty-printed compilation, tests, and model contracts. Done means a command like `spoon-test https://github.com/google/guava` runs all four checks without exceptions and reports failures clearly.

Written by the indexing model from the issue text.