fix: handle zero-length slice/subarray at end of multi-buffer

[mcollina]

Summary

• this is the dynamic-buffer side fix for the bug reported in platformatic/kafka#227 (deserialization failure under load)
• add regression tests for slice() and subarray() when called at the exact end of a multi-buffer DynamicBuffer
• fix both methods by returning early for zero-length ranges (start === end) before indexing into this.buffers[current]

Reproduction

This issue can be reproduced with:

const b = new DynamicBuffer([Buffer.from([1]), Buffer.from([2])])
b.slice(2) // throws TypeError before this fix

Same for b.subarray(2).

Verification

• npm test
• npm run lint