Replace global assert hook with static class member

[Gregox273]

Related Issue(s)	#4525
Has Unit Tests (y/n)	n
Documentation Included (y/n)	n
Generative AI was used in this contribution (y/n)	n

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Change Description

Replaces global pointer static AssertHook* s_assertHook with a static class member within AssertHook. This ought to address the SonarQube finding:

<High> Line 96: cpp:S5421 Global pointers should be const at every level.