feat: detect unsafe randomness and repeated storage reads

[Leothosine]

Summary

• Added UnsafeRandomnessRule that flags use of blockhash/block.timestamp as randomness sources and suggests VRF or commit-reveal alternatives.
• Added MultipleStorageReadsRule that detects repeated reads from the same storage slot and suggests local variable caching.

Changes

• packages/rules/src/security/randomness/unsafe_randomness.rs
• packages/rules/src/security/randomness/mod.rs
• packages/rules/src/optimization/storage/multiple_storage_reads.rs

closes #314
closes #315

[drips-wave]

@Leothosine Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits