more simplification of protobuf schema format (followups to 1488)

[cdisselkoen]

Description of changes

More simplifications of the Protobuf format for Schema, some suggested in #1488 and some based on conversations with @john-h-kastner-aws offline.

• resolving the TODO: Schema is just a list of EntityDecl and a list of ActionDecl, not a map, as this is simpler and sufficient
• removing the ability to have open attributes, as this is not a stable feature (in both entities and records)
• the context for an Action must be a record, so instead of Type, we require it to be a map<string, AttributeType>
• rename Type.Ty to Type.Prim which is more clear
• remove the Never, True, False, EmptySet, and AnyEntity types, as these should never appear in schemas
• remove the ActionEntity type as action entities can just be encoded as Entity type (we do not support action attributes in Protobuf, as that is not a stable feature)
• remove EntityRecordKind in favor of inlining it into Type
• a few field renumberings, which is a breaking change we can make now but not after stabilization

Issue #, if available

Checklist for requesting a review

The change in this PR is (choose one, and delete the other options):

• A change (breaking or otherwise) that only impacts unreleased or experimental code.

I confirm that this PR (choose one, and delete the other options):

• Updates the "Unreleased" section of the CHANGELOG with a description of my change (required for major/minor version bumps).

I confirm that cedar-spec (choose one, and delete the other options):

• Requires updates, and I have made / will make these updates myself. (Please include in your description a timeline or link to the relevant PR in cedar-spec, and how you have tested that your updates are correct.)

I confirm that docs.cedarpolicy.com (choose one, and delete the other options):

• Does not require updates because my change does not impact the Cedar language specification.

[github-actions]

Coverage Report

Head Commit: e47d8ac1b9dffb111c6b2d09aab66059f5bb400f

Base Commit: 25f7d950cadcfecddaecc2f3ba5af99a0adde0bf

Download the full coverage report.

Coverage of Added or Modified Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 0.00%

Status: FAILED ❌

Details

File	Status	Covered	Coverage	Missed Lines
cedar-policy/src/proto/validator.rs	🔴	0/53	0.00%	29-30, 42, 45, 92, 94-97, 104, 118-121, 167, 186-187, 189-191, 194-195, 197-200, 202-206, 208, 222-223, 226, 229, 232, 236, 239, 243-244, 246-250, 252-256, 258, 260

Coverage of All Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 85.50%

Status: PASSED ✅

Details

Package	Status	Covered	Coverage	Base Coverage
cedar-policy	🟢	10129/11618	87.18%	86.66%
cedar-policy-cli	🔴	526/912	57.68%	57.68%
cedar-policy-core	🟢	11947/14443	82.72%	82.72%
cedar-policy-formatter	🟢	907/1035	87.63%	87.63%
cedar-policy-validator	🟢	14290/15744	90.76%	93.15%
cedar-testing	🔴	0/426	0.00%	0.00%
cedar-wasm	🔴	0/29	0.00%	0.00%

[john-h-kastner-aws]

looks like our new coverage check is correctly complaining about the lack of tests for validator protobuf. should ofc add tests before stabilizing, but we can bypass for now