exercises: provide stubs for every exercise

[ee7]

Before this commit, the user-facing solution file was empty for every exercise apart from:

• clock
• dnd-character
• hello-world
• react

Add initial content to the user-facing solution file for every other exercise.

And check in CI that every exercise has a test file and stub that:

• compiles without error
• runs with an error (we want the stub to fail the tests)

Unfortunately, for now, this significantly increases the time taken to run CI (for the fastest exercises job: from about 25 seconds to about 4 minutes).

Closes: #409
Closes: #410

---

To-do:

• Rebase after merging exercises(darts): use separate parameters, not tuple #476

Some things left to consider:

• Rename lasagna parameters to match the docs
• Table vs CountTable vs array
• Remove range types?
• Parameters that want to have default values
• Parameter names
• Ways to speed up CI
  • actions/cache
  • Incremental compilation
  • Only run check_stubs.nim when one of these files changes: check_stubs.nim itself, an exercise stub, or an exercise test file
  • Make check_stubs.nim run only on Linux
  • Make check_stubs.nim run via a separate workflow

Policies:

• use proc, not func
• (todo)

For later PRs:

• Consider doc comments

[ee7]

CI log when stubs passed checks:

Checking stubs...
lasagna
acronym
all-your-base
[...]
two-fer
word-count
yacht

Success. Every exercise has a test file and stub that:
- compiles without error
- runs with an error (we want the stub to fail the tests)

Example CI log when bad stubs failed checks:

Checking stubs...
lasagna
test_lasagna.nim(4, 7) template/generic instantiation of `suite` from here
test_lasagna.nim(13, 8) template/generic instantiation of `test` from here
test_lasagna.nim(14, 5) template/generic instantiation of `check` from here
test_lasagna.nim(15, 7) Error: undeclared identifier: 'preparationTimeInMinutes'

acronym
[...]
collatz-conjecture
collatz_conjecture.nim(2, 1) Error: invalid indentation

crypto-square
[...]
gigasecond
gigasecond.nim(1, 25) Error: undeclared identifier: 'DateTime'

grade-school
grains
hamming
hello-world

[Suite] Hello World
  [OK] say hi!
Error: the hello-world stub passed the tests

high-scores
[...]
two-fer
test_two_fer.nim(4, 7) template/generic instantiation of `suite` from here
test_two_fer.nim(5, 8) template/generic instantiation of `test` from here
test_two_fer.nim(6, 11) Error: undeclared identifier: 'twoFer'

word-count
yacht

Error: there were 5 exercises with a problematic stub:
lasagna, collatz-conjecture, gigasecond, hello-world, two-fer

[ee7]

I was hoping to finish this a long time ago. Now that it's Mechanical March already, I'd like to merge this soon. Requested reviewers: could either of you check that the stubs look reasonable? I'll keep this as draft until I've fixed the names in lasagna.

CI does check that every exercise has a test file and stub that:

• compiles without error
• runs with an error (we want the stub to fail the tests)

[ErikSchierboom]

Fabulous!