Remove attr.cpp.archetype_eager codegen attribute

[Wumpf]

Related

• follow-up to Make all C++ archetypes eager serialized & provide generated update/clear APIs #8779

What

Makes eager serialization & update/clear apis the norm in C++ with no opt out.

Also removes no longer needed warning suppression on builder methods!

• said warning suppression is actually no longer needed on any compiler we test

[github-actions]

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Result	Commit	Link	Manifest
✅	76d2278	https://rerun.io/viewer/pr/8780	+nightly +main

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