Indexes 1: Change Package and related traits to not return references to fields

[dcookspi]

Note: for info on benefits of indexing for spk solves see #1340 (5 of 5). Maybe start there and work back down to this PR if you prefer to review PRs top down.

Changes various Package traits' methods to return Arc's instead of references to internal fields. This allows other package implementations, without matching fields, to use the traits. This is one of the changes that supports adding indexes and index based packages to Spk repositories.

This also adds the ArcCompat object as helper for serializing and deserializing Arc<Compat> fields.

This is 1 of 5 chained PRs for adding indexes to spk solves:

1. this PR
2. Indexes 2: Add new_unchecked() constructors to spk schema objects #1337
3. Indexes 3: Adds flatbuffers schema and SolverPackageSpec for indexes to spk #1338
4. Indexes 4: Adds Indexes for SPK repositories #1339
5. Indexes 5: Adds spk repo index subcommand for index generation and updates #1340

[codecov]

Codecov Report

❌ Patch coverage is 69.00000% with 31 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/spk-schema/src/arc_compat.rs	20.00%	12 Missing ⚠️
...schema/crates/foundation/src/spec_ops/versioned.rs	33.33%	2 Missing ⚠️
...schema/src/v0/embedded_recipe_install_spec_test.rs	0.00%	2 Missing ⚠️
crates/spk-schema/src/v0/embedded_recipe_spec.rs	50.00%	2 Missing ⚠️
crates/spk-schema/src/v0/platform.rs	33.33%	2 Missing ⚠️
...ates/spk-schema/src/v0/recipe_install_spec_test.rs	0.00%	2 Missing ⚠️
crates/spk-schema/src/v0/recipe_spec.rs	50.00%	2 Missing ⚠️
crates/spk-schema/src/v1/platform.rs	50.00%	2 Missing ⚠️
...ates/validation/src/validators/pkg_requirements.rs	0.00%	2 Missing ⚠️
crates/spk-schema/src/spec.rs	83.33%	1 Missing ⚠️
... and 2 more

📢 Thoughts on this report? Let us know!

[jrray]

We've discussed this elsewhere already, but for the record the suggestion is to use Cow instead of Arc to provide a way for some implementations to be able to return an owned value without sacrificing some places (like this one) from being able to return a cheap reference instead of cloning.

A perhaps even better alternative would be to change this method to return impl SomeNewTrait where that trait contains methods to access whatever is needed from whatever is currently calling this compat() method. Then implementers of Versioned are free to return anything that conforms to that trait.

[dcookspi]

Todo:

• Swap the updated Arc<..> return values out for Cow<..>.