[REQ] Unlink Container Formats from Compression and Encryption Algorithms

### Is your feature request related to a problem? Please describe
I'm unable to choose any combination of container format, compression algorithm, encryption algorithm.

### Describe the solution you'd like
Each time I create an archive, I'd like to:

1. Choose the container format.
2. Choose the compression algorithm.
3. Choose the encryption algorithm.

For example, instead of assuming that I want a `.tar.zst` when I choose ZSTD, I'd like to be able to choose each of the above to produce files like:

| Extension | Format |
|------------------------|----------------------------------|
| `.squashfs.zst` | SquashFS + Zstandard |
| `.tar.zst.age` | tar + Zstandard + age encryption |
| `.cpio.zst.age` | cpio + Zstandard + age |

### Describe alternatives you've considered
Using CLI utilities to create the archives by hand.

No implementation files or tests are named in the issue. Start by tracing Keka's archive-creation flow and how it currently selects container, compression, and encryption formats; done means users can choose each independently and create the listed combinations, including SquashFS/Zstandard and tar or cpio with Zstandard and age.

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