Add Memory Usage Calculation for eStore Data Structure

[sggeorgiev]

Overview

Introduces comprehensive memory usage tracking for ebuckets and estore data structures to enable better memory profiling and optimization.

Changes

ebMemUsage(): Calculates memory footprint of individual ebuckets instances
estoreMemUsage(): Calculates total memory usage across all buckets in an estore

Key Features

Stack Type: Recursively calculates L1/L2 levels plus L3 vector segments
Rax Type: Accounts for rax structure, nodes, keys, and segment headers
List Type: Returns 0 (items stored inline)
Empty Buckets: Fast-path returns 0
Cluster-aware: Optimized calculation for clustered vs non-clustered modes

Test Coverage

✅ Empty buckets return 0
✅ List-based buckets return 0 (inline storage)
✅ Rax-based buckets with multiple segments
✅ Extended segments with NextSegHdr
✅ Stack-based buckets with L1/L2/L3 levels

Use Cases

Memory profiling and debugging
Resource usage monitoring
Performance optimization analysis