compute blob tx KZG commitments once per test class

[macfarla]

The 4 blob transaction fields in AbstractTransactionPoolTestBase were instance fields, causing ~1980 native KZG JNI operations per test run of LegacyTransactionPoolGasPriceTest (3 calls × 6 blobs × 2 ops × 55 test instances). Each BlobTestFixture starts from byteValue=0x00, so all instances produced identical blob data.

Make the 4 blob transaction fields static final, computed once at class load via private static factory methods. The existing instance methods are retained for TransactionPoolSaveRestoreTest which calls createBlobTransaction() at test-method time with the real blockGasLimit.
AbstractTransactionPoolTestBase.java

• Added private static final BlobTestFixture BLOB_TEST_FIXTURE — shared fixture initialized once
• Changed 4 blob transaction fields from protected final → protected static final, calling new private static factory methods
• Added createStaticBlobTransaction, createStaticBlobTransactionWithSameBlobs, createStaticReplacementTransactionWithBlobs — private static methods using gasLimit(0L) (same as the instance fields got anyway, since blockGasLimit=0 at init time)
• Kept the existing instance methods (createBlobTransaction, etc.) for TransactionPoolSaveRestoreTest which legitimately calls them at test-run time
• Removed the null checks from the instance methods (they now use the shared static BLOB_TEST_FIXTURE)

Net effect: 1,980 native KZG JNI operations per test run → 36.

Locally, you can run these tests to catch failures early:

• spotless: ./gradlew spotlessApply
• unit tests: ./gradlew build

[Copilot]

Pull request overview

This PR reduces expensive native KZG JNI work in transaction pool tests by caching blob-transaction test fixtures at class-load time rather than per test instance.

Changes:

• Converted blob-related transaction fixtures from instance fields to static final fields computed once.
• Introduced private static factory methods for creating the cached blob transactions.
• Switched instance-time blob transaction creation to use a shared static final BlobTestFixture.

[macfarla]

old time:

BUILD SUCCESSFUL in 3m 27s
68 actionable tasks: 68 executed
Consider enabling configuration cache to speed up this build: https://docs.gradle.org/9.3.1/userguide/configuration_cache_enabling.html
./gradlew :ethereum:eth:test --tests "*LegacyTransactionPoolGasPriceTest*"   1.27s user 0.22s system 0% cpu 3:28.55 total

new time:

BUILD SUCCESSFUL in 2m 5s
68 actionable tasks: 68 executed
Consider enabling configuration cache to speed up this build: https://docs.gradle.org/9.3.1/userguide/configuration_cache_enabling.html
./gradlew :ethereum:eth:test --tests "*LegacyTransactionPoolGasPriceTest*"   1.13s user 0.20s system 1% cpu 2:06.26 total

and there are 4 classes that extend from this same Abstract class

[usmansaleem]

LGTM