Enable Typescript "strict" mode across the repo

[tsa96]

When we started the rewrite we didn't enable "strict": true in our tsconfigs, which was a mistake. It provides much stronger type-checking, especially for forcing you to handling possible undefined and nulls better.

I had a quick go and switching over when doing the Nx migration but found class-validator too annoying and forgot about it. Sikari in Discord recommends these settings

"strict": true,
"downlevelIteration": true,
"emitDecoratorMetadata": true,
"experimentalDecorators": true,
"strictPropertyInitialization": false,

Let's aim to get "strict": true in our root tsconfig.json and any projects that really need it disabled (maybe backend E2E tests) can override in their own tsconfig. If we can do E2E tests as well then great, but doesn't matter at all as much. Most of our libraries are using strict mode already, but frontend and backend apps have it off:

• apps/frontend
• apps/frontend-e2e
• apps/backend
• apps/backend-e2e (can maybe ignore)
• libs/frontend/data
• libs/frontend/directives
• libs/frontend/icons
• libs/frontend/env
• libs/frontend/pipes
• libs/frontend/theme
• libs/backend/config
• libs/backend/decorators
• libs/backend/dto
• libs/backend/pipes
• libs/backend/test-utils
• libs/backend/validators
• libs/bitflags
• libs/constants
• libs/enum
• libs/random
• libs/replay