refactor!(core): rework attribute semantics

[imrn99]

Sorry for the size of the last 2 PRs!

New semantic over attributes:

• try / regular / force for merges & splits (same as (un)sews, see refactor!(core): rework sew methods to allow for more control #224)
• regular / force for RW accesses (same as (un)links, see refactor!(core): rework sew methods to allow for more control #224)
• RW access methods are now limited to:
  • read: read a value
  • write: (over)write a value, returning the old one
  • remove: remove a value, returning it

Done:

• add a new enum, CMapError
• add type alias CMapResult<T> = Result<T, CMapError>
• update embed methods to use the new semantic
• update the AttributeStorage<A> & UnknownAttributeStorage to use the new semantic
  • also update the trait implementation for AttrSparseVec
• update AttrStorageManager to use the new semantic
• update the documentation with explanation over the new semantic

Follow-up:

• add tests over edge case allowed by the new semantics (e.g. a potential transaction cancel over some concurrent changes)
• replace some options with with CMapResult<A> where possible / coherent
  • this corresponds mostly to places with CMapResult<Option<A>>
• update AttributeUpdate fallback methods to return CMapResult<Self>
  • this creates even more control, with some attributes being essential and others fail-proof

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.66185% with 310 lines in your changes missing coverage. Please review.

Project coverage is 79.21%. Comparing base (81f9a53) to head (d5d4831).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
honeycomb-core/src/attributes/manager.rs	42.42%	171 Missing ⚠️
honeycomb-core/src/attributes/collections.rs	50.60%	41 Missing ⚠️
honeycomb-core/src/cmap/dim2/embed.rs	30.90%	38 Missing ⚠️
honeycomb-core/src/cmap/dim2/sews/two.rs	47.27%	29 Missing ⚠️
honeycomb-core/src/cmap/dim2/sews/one.rs	46.66%	8 Missing ⚠️
honeycomb-kernels/src/grisubal/routines/clip.rs	0.00%	8 Missing ⚠️
honeycomb-core/src/attributes/traits.rs	50.00%	6 Missing ⚠️
honeycomb-core/src/cmap/error.rs	0.00%	3 Missing ⚠️
honeycomb-core/src/cmap/dim2/links/one.rs	0.00%	2 Missing ⚠️
honeycomb-core/src/cmap/dim2/links/two.rs	0.00%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #226      +/-   ##
==========================================
- Coverage   80.67%   79.21%   -1.46%     
==========================================
  Files          51       52       +1     
  Lines        6850     6953     +103     
==========================================
- Hits         5526     5508      -18     
- Misses       1324     1445     +121     

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[cedricchevalier19]

Looks ok, I will mainly trust the Rust toolchain on this PR.

[cedricchevalier19]

I do not really follow? Do you mean that even if the result value is not interesting, the user has to check if ok?

[imrn99]

I believe the stm crate uses these errors to detect invalid transaction (early?), so yes, the ? operator should be called on every results inside a transaction, including Result<(), StmError>.

[imrn99]

Looks ok, I will mainly trust the Rust toolchain on this PR.

We can set something up this week to go over the API and any questions / shortcomings.