refactor(error)!: handle errors more gracefully in rustic_core.

[simonsan]

Till now, rustic_core had a lot of unwraps and expects sprinkled over the code base. This made rustic_core and dependents panic in case of errors. This is unacceptable for a library, hence we fixed it now.

Fixes #140

TODO:

• [X] Implement unit tests for test coverage of some changes
• [x] Fix integration test
• [x] 0 (*nix) errors left (due to unwrap/expect being denied)

Possible Panics left over/reintroduced:

• HexId::as_str() / Id:to_hex(): Commit cc6430f4

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 26.00000% with 444 lines in your changes missing coverage. Please review.

Project coverage is 27.5%. Comparing base (fb291dc) to head (f1218c8). Report is 106 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/core/src/commands/restore.rs	0.0%	123 Missing :warning:
crates/core/src/blob/packer.rs	54.4%	61 Missing :warning:
crates/core/src/commands/prune.rs	4.3%	44 Missing :warning:
crates/core/src/vfs.rs	0.0%	29 Missing :warning:
crates/core/src/backend/local_destination.rs	15.1%	28 Missing :warning:
crates/core/src/backend/cache.rs	0.0%	24 Missing :warning:
crates/core/src/blob/tree.rs	32.1%	19 Missing :warning:
crates/core/src/commands/copy.rs	0.0%	17 Missing :warning:
crates/core/src/commands/forget.rs	0.0%	15 Missing :warning:
crates/core/src/archiver.rs	45.8%	13 Missing :warning:
... and 21 more

Additional details and impacted files

Files with missing lines	Coverage Δ
crates/backend/src/choose.rs	0.0% <ø> (ø)
crates/backend/src/opendal.rs	0.0% <ø> (ø)
crates/backend/src/rclone.rs	87.5% <ø> (+9.7%)	:arrow_up:
crates/core/src/archiver/file_archiver.rs	77.0% <ø> (ø)
crates/core/src/cdc/polynom.rs	75.0% <ø> (ø)
crates/core/src/cdc/rolling_hash.rs	54.3% <ø> (ø)
crates/core/src/chunker.rs	58.6% <ø> (+0.7%)	:arrow_up:
crates/core/src/crypto/aespoly1305.rs	77.7% <ø> (-5.6%)	:arrow_down:
crates/core/src/error.rs	25.0% <ø> (+10.7%)	:arrow_up:
crates/core/src/index/binarysorted.rs	54.5% <ø> (-0.9%)	:arrow_down:
... and 36 more

... and 7 files with indirect coverage changes

[simonsan]

The CI fails for Test Coverage, I don't intend to write tests at this stage for the changes as I think we should focus on the other tests first, that we wanted to implement (e.g. path related stuff).

I don't want to implement these tests in this PR though, as it's already quite big.

[simonsan]

OK, added some more testing, so the coverage test also runs through. 👍🏽

[simonsan]

Closing this as it's heavily outdated.