fix(tests): address review feedback on enhanced ported static tests

[spencer-tb]

Description

Review feedback for ethereum#3215.

Discrimination restored

• test_non_zero_value.py: call success flag stored inside the CodeGasMeasure window, a failed call was gas-identical to success for CALLCODE/DELEGATECALL
• test_raw_call_gas_ask.py: caller side slot restored (unused 63/64 gas credited back), fork derived
• test_make_money.py: original gas=2**256-20 ask restored, the clamp is the subject
• test_copy_offset.py: nonzero tx calldata so a wrong in-bounds offset is observable

Coverage

• test_add_non_const.py: drop stale pre_alloc_mutable (execute-mode skip), canary slot, floor to Frontier
• test_delegatecall_emptycontract.py: pin empty: Account.NONEXISTENT

Cleanup

• name magic operands (FORWARDED_GAS/GAS_SLOT), drop dead _SIZE_LABEL, assert available > 0 budget guard
• placeholder/stale docstrings rewritten

Skill

• add: budget-vs-subject gas operands, zero-source-data trap, count-the-old-post's-slots, success-flag trap, final sweep checklist

Related Issues or PRs

ethereum#3215.

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.

Cute Animal Picture