Dynamic storage: Charge gas for new bytes properly

[Dentosal]

Follow-up to: #982

Part of: #987

Checklist

• Breaking changes are clearly marked as such in the PR description and changelog
• New behavior is reflected in tests
• If performance characteristic of an instruction change, update gas costs as well or make a follow-up PR for that
• 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

High Risk
Changes gas metering for dynamic storage opcodes, which is consensus/validity-critical and can alter transaction acceptance and execution costs. Adds a new in-VM cache that affects charging behavior across repeated writes within an execution.

Overview
Fixes dynamic storage gas accounting so SWRD/SWRI and SUPD/SUPI charge additional new_storage_per_byte gas only for bytes that grow a slot, not for overwrites.

Adds an Interpreter-level storage_slot_size_cache keyed by (ContractId, Bytes32) and updates storage read/write/update/preload paths to populate it and use it when computing “new bytes” charges; dynamic storage opcode execution is refactored to call new helper methods (dynamic_storage_read/write/update) that encapsulate the updated gas charging.

Updates tests by raising a helper script gas limit and adding a regression test asserting the second write of the same length uses BYTES_TO_WRITE less gas than the first; includes a changelog entry.

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[Dentosal]

Closing in favor of #996