refactor(test-benchmark): centralize benchmark helper utilities

[LouisTsai-Csie]

Description

Consolidates the three scattered helpers.py modules (tests/benchmark/compute/helpers.py, tests/benchmark/stateful/helpers.py, and the shared parts of tests/benchmark/stateful/eip7928_block_level_access_lists/helpers.py) into the existing shared package tests/benchmark/helper/, organized by domain:

Module	Contents
numeric.py	Numeric / stack helpers (neg, sar, make_dup, DEFAULT_BINOP_ARGS, …)
enums.py	Parametrization enums (StorageAction, ReturnDataStyle, CacheStrategy, TransactionResult)
loops.py	Loop-construction bytecode (DECREMENT_COUNTER_CONDITION)
precompile.py	Precompile opcode targets, calculate_optimal_input_length
contract_factory.py	CustomSizedContractInitcode / CustomSizedContractFactory, ContractDeploymentTransaction
transactions.py	build_benchmark_txs, pack_transactions_into_blocks, build_cache_strategy_blocks
storage.py	SSTORE initializers, StorageInitRange, build_sequential_storage_init, calldata/access-list generators
delegation.py	EIP-7702 delegation setup, run_bloated_eoa_benchmark

• primitives: numeric, enums)
• building blocks: loops,precompile, contract_factory, transactions, storage, account_creator, account_sender_receiver
• scenario runners: delegation

Cleanups included in the PR:

• Removed unused symbols: CallDataOrigin, concatenate_parameters (also drops the cross-suite tests.osaka import it required), ALLOWANCE_SELECTOR, MINT_SELECTOR.
• Moved the remaining ERC20 selectors into test_erc20.py, their only consumer.

No test logic changes within this PR, only code refactor.

Related Issues or PRs

Issue #2625

Checklist

• Ran fast static checks to avoid CI fails, see Code Standards & Verifying Changes: just static
• PR title has the form <type>(<area>): <title>, where <type> and <area> come from an appropriate C-<type>, respectively A-<area>, label. The title should match the target squash commit message.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

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[spencer-tb]

Refactor is clean. Easy to approve here!