Standardise toolchains with .tool-versions and verify builds in CI

[adamnfish-gu]

The example skeleton projects all use their own approach to setting up their language toolchains. Many use brew, which will only work on a Mac, but there are other approaches including assuming the tools are already available.

Additionally, lots of the projects are very out of date, and will no longer build. Ideally we'd know about this automatically ahead of time.

This issue tracks the work to fix that.

See also: #142

Approach

• Each project declares its toolchain in a .tool-versions file, pinned to the major version (e.g. java 21, sbt 1).
• script/setup runs the project's own dependency-fetch command, which populates their caches and ensures the language build tools defined in .tool-versions are available.
• script/test runs a trivial passing testuite in the example skeleton project, which ensures the project builds and runs. These test scripts are now consistent so this can be run from CI.
• The root README recommends mise for reading those files, but any version manager that understands .tool-versions would work.
• CI discovers projects by looking for a .tool-versions file. CI also includes a step that fails the build if a project declares a toolchain without also providing the standard script/setup and script/test scripts.

PRs

The platform PR sets up CI and the documentation, all the language specific PRs build on top of it. Projects are independent of each other, but within a project fix must merge before adopt. Where languages include multiple PRs (a fix PR separate to an adopt PR), these have been "stacked" in GitHub.

Platform — the CI workflow and README updates:

• Add CI workflow and document .tool-versions toolchain setup #144 Add the CI workflow and document mise

Per project — fix makes the project builds and the tests pass ,adopt adds .tool-versions and updates script/setup:

• scala
  • fix scala: Make the scala example test pass and script/test CI-friendly #145
  • adopt scala: Declare the scala toolchain in .tool-versions #146
• java
  • adopt java: Declare the java toolchain in .tool-versions #147
• rust
  • adopt rust: Adopt .tool-versions and standardise scripts for Rust #148
• swift
  • adopt swift: Adopt .tool-versions and scripts-to-rule-them-all for swift #149
• python
  • fix python: Fix failing example test in test_pairing_exercise.py #150
  • adopt python: Adopt .tool-versions and standardise script/ for Python #151
• ruby
  • fix ruby: Fix returnsFalse returning true and remove print from initialize #152
  • adopt ruby: Adopt .tool-versions and standardise script/setup for ruby #153
• javascript
  • fix javascript: Fix failing test and make script/test exit non-interactively #154
  • adopt javascript: Adopt .tool-versions and standardise scripts #155
• javascript-esm
  • fix javascript-esm: Fix failing test and non-terminating test runner #156
  • adopt javascript-esm: Adopt .tool-versions toolchain declaration for javascript-esm #157
• typescript-deno
  • fix typescript-deno: Fix failing test, watch-mode default, and update imports for Deno 2 #158
  • adopt typescript-deno: Adopt .tool-versions and standardise script/ for Deno 2 #159
• typescript-node
  • fix typescript-node: Fix yarn lockfile, test value, and script/test for CI #160
  • adopt typescript-node: Declare the typescript-node toolchain in .tool-versions #161
• go
  • fix go: Fix build: add go.mod, proper imports, and make test pass #162
  • adopt go: Adopt .tool-versions and standardise setup script #163
• kotlin
  • fix kotlin: Upgrade Gradle, Kotlin, and JUnit to work on JDK 21 #164
  • adopt kotlin: Adopt .tool-versions and standardise setup scripts #165
• dot-net-core
  • fix dot-net-core: Fix build and failing test for .NET 10 #166
  • adopt dot-net-core: Adopt .tool-versions and standardise scripts for dot-net-core #167
• clojure
  • fix clojure: Upgrade Clojure 1.6 to 1.11.1 and fix failing example test #168
  • adopt clojure: Declare the clojure toolchain in .tool-versions #169
• php
  • fix php: Fix skeleton test to pass and expose testable code #170
  • adopt php: Adopt .tool-versions and standardise setup scripts #171

Notes

• java, rust and swift have no fix PR: their tests already pass on main.
• typescript-node's fix PR is large even though there are only a few changes. This is because of the Yarn zero-install cache regeneration, which is unavoidable because the committed lockfile is stale.
• The clojure project was nested one directory deeper than every other skeleton. Its adopt PR unnests it, so that the CI discovery works.

The expected end state (with every project change included) is on integration/verify. That branch is pushed so we can see the whole change at once if that's useful, it shouldn't be merged.