Fix lockfile usage and updating

[CSVdB]

resolveFlake must be able to handle 6 use cases for what to do with the lockfile:

1. prim_getFlake while pure: In this case, everything is handled purely, so no registries, no updating LockFile, no writing LockFile to file.
2. nix build dwarffs: Update LockFile before usage
3. nix build ~/nix/dwarffs: Update LockFile before usage, and save it to file. This is only if the installable is a FlakeRef with IsPath.
4. nix build ~/nix/dwarffs --no-save-lock-file: Update LockFile before usage, and don't save it to file
5. nix build X --recreate-lock-file: Same as above (depending on what X is), but recreate the LockFile from scratch
6. nix flake update: Same as case 5

In order to implement this, I will create an enum

enum HandleLockFile { AllPure, UpdateLockFile, UseUpdatedLockFile, RecreateLockFile, UseNewLockFile};

with two helper functions

bool allowedToWrite (HandleLockFile handle);
bool recreateLockFile (HandleLockFile handle);

resolveFlake now gets an argument HandleLockFile.