Disable limited-tx-count feature when running benchmarks

[Dentosal]

Description

The limited-tx-count feature in fuel-core-executor caps max_tx_count() at 1024. It was being activated in the benchmark binary via: benches → test-helpers → fuel-core-executor[limited-tx-count].

This caused blocks to be limited to 1024 user transactions, which causes benchmarks to fail.

The tests/Cargo.toml independently enables limited-tx-count in its own dev-deps, so the blocks.rs test that calls max_tx_count() remains correct. Tests crate enables it directly. The test-helpers dep on limited-tx-count was redundant and was only causing the transitive contamination into the benchmarks.

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• I have reviewed the code myself
• I have created follow-up issues caused by this PR and linked them here

[cursor]

PR Summary

Low Risk
Manifest-only change that removes an unintended feature flag; risk is limited to build/feature resolution differences in test/bench crates.

Overview
Removes the fuel-core-executor dependency with the limited-tx-count feature from tests/test-helpers/Cargo.toml, preventing that feature from being enabled transitively in downstream consumers (e.g., benchmarks).

This avoids accidentally capping block transaction counts during benchmarking while leaving any explicit test-only enabling of limited-tx-count to other crates.

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