Avoid some instances of boxing

[SolalPirelli]

Notes for myself when I come back from vacation:

• caffc6e breaks compat; worth partial revert, but keep the NameTable removal as it's really leaky anyway
• I think I forgot to push one commit (the one with hashing products for namekinds)

Looking at a helloWorld flame graph for 100 iterations at a time, I noticed 1.5% was in integer boxing, so decided to look further.

Self-contained commits, probably best to review commit-by-commit.

Have you relied on LLM-based tools in this contribution?

No

How was the solution tested?

Covered by existing tests (this is a refactoring)

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