fix[OA-audit-N15]: Use of magic numbers

[md0x]

Signed-off-by: Pablo Maldonado pablo@umaproject.org

Motivation

OZ identifies the following issue:

The OptimisticAsserter and FullPolicyEscalationManager contracts use the
constant value 1e18 in the settleAssertion and getPrice functions without
documenting the value's meaning.
Literal values in the codebase without an explained meaning make the code harder to
understand and maintain, thus hindering the experience of developers, auditors, and external
contributors alike. To improve the code's readability and facilitate refactoring, consider defining
a constant for every magic number, giving it a clear and self-explanatory name.

Summary

Add constant variable representing the numerical true value

[Reinis-FRP]

Should we better use capitalized version NUMERICAL_TRUE

[chrismaree]

wellll...they did raise this on the N-02 Constant not using UPPER_CASE format and I specifically pushed back on that for the case of defaultIdentifier as I did not want the public interface for this to be upper case when we have defaultCurrency as well as defaultLiveness not being upper case. there is an argument to go against the solidity styling guide for consistency within our own contract