Cleanup Move warnings in Governed Gas Pool module and spec

[andygolay]

Description

• Clean up various Move warnings in governed_gas_pool.move and governed_gas_pool.spec.move

Type of Change

• New feature
• Bug fix
• Breaking change
• Performance improvement
• Refactoring
• Dependency update
• Documentation update
• [ x] Tests

Which Components or Systems Does This Change Impact?

• Validator Node
• Full Node (API, Indexer, etc.)
• Move/Aptos Virtual Machine
• [ x] Aptos Framework
• Aptos CLI/SDK
• Developer Infrastructure
• Other (specify)

How Has This Been Tested?

movement move test

Key Areas to Review

Checklist

• [x ] I have read and followed the CONTRIBUTING doc
• [ x] I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• [ x] I identified and added all stakeholders and component owners affected by this change as reviewers
• I tested both happy and unhappy path of the functionality
• [ x] I have made corresponding changes to the documentation

Outstanding issues:

In aptos-move/e2e-move-tests, cargo test fails with an unrelated error that also appears in the Aptos Labs aptos-core repo. Issue opened here: #130