View, create and edit (typing) tests

backend/app/crud/tests.py

backend/app/routes/tests.py

frontend/src/lang/fr.json

frontend/src/lib/api/tests.ts

frontend/src/lib/components/tests/TestForm.svelte

frontend/src/lib/types/tests.ts

frontend/src/routes/admin/studies/+page.svelte

frontend/src/routes/admin/studies/new/+page.server.ts

frontend/src/routes/admin/tests/+page.svelte

frontend/src/routes/admin/tests/+page.ts

frontend/src/routes/admin/tests/[id]/+page.server.ts

frontend/src/routes/admin/tests/[id]/+page.svelte

frontend/src/routes/admin/tests/[id]/+page.ts

frontend/src/routes/admin/tests/new/+page.server.ts

frontend/src/routes/admin/tests/new/+page.svelte