TPE: Guard against stack overflow

[luxas]

Description of changes

Broken out from #2162.
I noticed this mis-match in behavior between normal eval and partial eval, so adding the stack overflow guard to TPE as well.

Issue #, if available

Checklist for requesting a review

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

• A change "invisible" to users (e.g., documentation, changes to "internal" crates like cedar-policy-core, cedar-validator, etc.)

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• Does not update the CHANGELOG because my change does not significantly impact released code.

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• Does not require updates because my change does not impact the Cedar formal model or DRT infrastructure.

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

[github-actions]

Coverage Report

Head Commit: d5b53d31d8c13687742d2ff9d03a1d90e4f3cd25

Base Commit: 03d1ca290f0c27afbb138c6c69990ec801944c4b

Download the full coverage report.

Coverage of Added or Modified Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 75.00%

Status: FAILED ❌

Details

File	Status	Covered	Coverage	Missed Lines
cedar-policy-core/src/evaluator.rs	🟢	1/1	100.00%
cedar-policy-core/src/tpe/evaluator.rs	🔴	2/3	66.67%	68

Coverage of All Lines of Rust Code

Required coverage: 80.00%

Actual coverage: 87.65%

Status: PASSED ✅

Details

Package	Status	Covered	Coverage	Base Coverage
cedar-language-server	🟢	4722/5102	92.55%	92.55%
cedar-policy	🟡	4227/5353	78.97%	78.97%
cedar-policy-cli	🟡	1210/1614	74.97%	74.97%
cedar-policy-core	🟢	24010/27282	88.01%	88.01%
cedar-policy-formatter	🟢	914/1088	84.01%	84.01%
cedar-policy-symcc	🟢	6752/7262	92.98%	92.98%
cedar-wasm	🔴	0/28	0.00%	0.00%

[luxas]

I didn't see any unit tests for this in the real evaluator, so do we add something to both places, or just ignore the coverage check for the modified lines?

[john-h-kastner-aws]

I didn't see any unit tests for this in the real evaluator, so do we add something to both places, or just ignore the coverage check for the modified lines?

We probably didn't have the coverage checks when we added the guard to the evaluator, but I'm fine with leaving it uncovered.

[luxas]

Cool, then we can merge this 👍 Does GitHub let us merge this even though one check is failing? 🤔