refactor(database): extract duplicate test balance constants

[futreall]

Replace duplicate BENCH_TARGET_BALANCE and BENCH_CALLER_BALANCE constants with a shared COMMON_TEST_BALANCE constant to improve maintainability.

Both constants had identical values: U256::from_limbs([10_000_000_000_000_000, 0, 0, 0])

This change:

• Eliminates code duplication
• Makes balance changes easier to maintain
• Preserves all existing functionality
• Only affects test/benchmark constants

[codspeed-hq]

CodSpeed Performance Report

Merging #3017 will not alter performance

_{Comparing futreall:refactor/extract-common-test-balance (27dc07a) with main (b7cb54f)}

Summary

✅ 173 untouched

[rakita]

nit pending

[futreall]

thanks!

[rakita]

tests fixed on main