fix: make example solutions compile with V 0.5.2

[metif12]

What

Three example/test files that no longer compiled against a current V. Split out of #307 so it can be reviewed and merged on its own.

Exercise	Problem	Fix
allergies	sorted_with_compare() on a []Allergen makes V emit calls to the builtin compare(int*, int*); the C backend rejects the pointer types.	run_test.v sorts a mapped []int instead, so no custom compare is needed.
intergalactic-transmission	u8 << int is now widened to int, so add_parity(current) received an int where a u8 is required.	Cast the packed byte back with u8(...).
zebra-puzzle	constraint !in queue.array() — the in operator on an array of structs generates an int vs struct comparison in C.	Replaced with an explicit .any() predicate over the fields that identify a constraint.

Verification

Verified on both ends of the supported version range, so this is safe to merge independently of a V upgrade in the test runner:

• bin/verify-exercises-in-docker (the current vlang-test-runner image, V 0.4.8): all three pass.
• V 0.5.2, the version vlang/setup-v installs for bin/test in CI: all three pass.

configlet lint passes, and v fmt -l / v vet are clean on the touched files.

Note for the merge commit

Please do not add [no important files changed]. These three exercises previously failed to compile, so students' existing solutions for them get re-tested and can now report a real result instead of a build error.

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

For more information, refer to the documentation. If you are unsure whether to add the message or not, please ping @exercism/maintainers-admin in a comment. Thank you!