securely copying or moving files between vaults without the android integrated share-feature

### Please agree to the following

- [x] I have searched [existing issues](https://github.com/cryptomator/android/issues?q=) for duplicates
- [x] I agree to follow this project's [Code of Conduct](https://github.com/cryptomator/android/blob/develop/.github/CODE_OF_CONDUCT.md)

### Summary

A feature that allows to internally download files from a vault and copy or move them to another directly and without storing them unencrypted in some system cache.

### Motivation

When copying multiple files from an online to a local vault could either be done with the export or the share feature. Export requires saving the files unencrypted on the drive, the share feature doesn't provide a download progress bar and the share menu just pops up, after all files are cached locally (and insecurely) not allowing the user to see the progress made.

Ideal would be to be able to select another vault (the vault would have to be open) when files are selected for moving and copying and select a location in the second vault as target. Then implementing the progress bar again, maybe with three steps per file, downloading, decrypting and encrypting again.

### Considered Alternatives

Maybe integrate an opened cryptomator vault into the explorer so that it can be selected with the export feature?

### Anything else?

_No response_