fix tc step types

[rsoeldner]

This PR enhances the typechecking for defpacts by ensuring consistency in return types across all steps. Previously, varying return types were permissible for each step. This update mandates that the return type for all steps aligns with the defpact's defined result type.

PR checklist:

• Test coverage for the proposed changes
• PR description contains example output from repl interaction or a snippet from unit test output
• Documentation has been updated if new natives or FV properties have been added. To generate new documentation, issue cabal run tests. If they pass locally, docs are generated.
• Any changes that could be relevant to users have been recorded in the changelog
• In case of changes to the Pact trace output (pact -t), make sure pact-lsp is in sync.

Additionally, please justify why you should or should not do the following:

• Confirm replay/back compat
• Benchmark regressions
• (For Kadena engineers) Run integration-tests against a Chainweb built with this version of Pact

[emilypi]

I'd like to see a regression that addresses nested defpacts in here.

[rsoeldner]

I'd like to see a regression that addresses nested defpacts in here.

This PR concentrates solely on ensuring that each step's result type is consistent with the overall defpact type. While Stuart's nested defpact example remains a separate challenge, it is regarded as an independent issue and will be addressed in a future PR. This current update is dedicated to aligning step result types with the defpact's defined type.

[jwiegley]

What does this binding do, and how is it extending the test? Is this suggesting that the return type of test-pact-guards should be :string?

[rsoeldner]

step has return type string, with this change, we enforce that all steps have the same return type. Hence, the change will return the "step2" string. This is a fix to a pre-existing test (on caps).

[jwiegley]

Could you please add some comments to the test describing what's going on here and what exactly is being tested by these odd constructions? (Namely, binding to a name that is never used). Everything else looks good!