New crate: mollusk-svm-on-demand

[L0STE]

This crate simplifies testing by fetching and storing mainnet accounts directly in the AccountStore.

Key Features

The new RpcAccountStore allows you to:

• Pass mock accounts using the with_accounts method
• Fetch mainnet accounts from instructions using the from_instruction method to automatically dump all accounts referenced in an instruction
• Handle missing accounts gracefully with the allow_missing_accounts method, which stores them with default values
• Add CPI programs using the add_programs method, which fetches program data from the account store and loads it via mollusk.add_program_with_elf_and_loader (supports both loader V2 and V3)
• Sync slots with mainnet using with_synced_slot for oracles that require the current mainnet slot to function correctly

New Harness

Added a new test harness variant with *_with_context methods that implement all the above helpers. These methods support both strict and non-strict modes depending on how they're called, while maintaining the same interface as the original harness.