Make KZG precompute value configurable

[jtraglia]

PR Description

Allow users to configure KZG libraries with a new hidden --Xkzg-precompute flag.

For reference, see: https://github.com/ethereum/c-kzg-4844/blob/main/README.md#precompute

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

[StefanBratanov]

LGTM

[cursor]

Bug: RustKZG Incorrectly Converts Integer to Boolean

The RustKZG implementation incorrectly converts the kzgPrecompute integer parameter to a boolean (kzgPrecompute != 0). This leads to inconsistent behavior with the CKZG4844 implementation, which passes the exact integer value. This contradicts CLI documentation stating values 0-15 provide fine-grained control over performance/memory. As a result, RustKZG treats all non-zero values identically (e.g., 5 vs. 10), contrary to user expectations for distinct effects.

infrastructure/kzg/src/main/java/tech/pegasys/teku/kzg/RustKZG.java#L56-L58

teku/infrastructure/kzg/src/main/java/tech/pegasys/teku/kzg/RustKZG.java

Lines 56 to 58 in 3f81433

	try {
	final boolean usePrecompute = kzgPrecompute != 0;
	this.library = new LibEthKZG(usePrecompute);

Fix in Cursor • Fix in Web

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