Bang-pattern on applyContToValue's value argument

[edmundnoble]

This ensures more robustly that all of the work done by an expression is done by the time it returns, though still some care is needed for the more nested Pact value types.

PR checklist:

• Test coverage for the proposed changes
• PR description contains example output from repl interaction or a snippet from unit test output
• (If Relevant) Documentation has been (manually) updated at https://docs.kadena.io/pact

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

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