Formal verification: native token balance updates

[mmv08]

This PR:

• Adds a rule for which methods can update the native token balance
• Adds a unit test rule per particular method
• Adds getStorageAt to the list of unreachable methods because it doesn't work with storage hooks

[github-actions[bot]]

Pull Request Test Coverage Report for Build 5156037295

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.8%

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Totals
Change from base Build 5134646122:	0.0%
Covered Lines:	308
Relevant Lines:	330

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💛 - Coveralls