Consider changing some internal services to singletons

[nfroidure]

Some services, like $fatalError should probably be singletons since they concern the processes (its only use is atm here: https://github.com/nfroidure/common-services/blob/main/src/process.ts#L84-L88

Some other ain't that simple to determine INJECTOR and SILO_CONTEXT are not singletons and it looks difficult to change their nature: https://github.com/nfroidure/knifecycle/blob/86a34ca367a13cbfa62def2a98bca0a5d0fdd180/src/index.ts#L397-L398

Maybe that the autoloader itself should not be a singleton and be tied to its silo context? That said since initializers are the same for all silos, the autoloader would be a singleton that finally load the same things for each silos? Weird... Or not?

Have to think about it more, let's not include it into the v16.

[nfroidure]

$fatalError is now a singleton and a separate file in the codebase https://github.com/nfroidure/knifecycle/blob/main/src/fatalError.ts#L56