Add logical size tracking for SET and HASH hashtable encoding

[liorsve]

Summary

Adds incremental logical size tracking for hashtable-encoded SET and HASH data types. The hashtable struct maintains a tracked_data_bytes field that is automatically updated on every insert/remove, giving O(1) access to the total logical entry size without walking the table.

Hashtable changes (hashtable.c/hashtable.h)

• Added entryGetSize callback to hashtableType — returns logical size of an entry
• Added tracked_data_bytes field to struct hashtable, maintained automatically on insert(), hashtableInsertAtPosition(), hashtablePop(), hashtableTwoPhasePopDelete(), hashtableEmpty()
• Added hashtableTrackedDataBytes() accessor and hashtableAdjustTrackedDataBytes() for in-place entry mutations

SET tracking (server.c)

• Added sdsEntryGetSize callback: sdsHdrSize(type) + sdslen(s) + 1 — pure arithmetic, no zmalloc calls
• Wired into setHashtableType
• Fully automatic — zero changes to t_set.c

HASH tracking (entry.c, server.c, t_hash.c)

• Added entryGetLogicalSize() in entry.c covering all 4 entry types (TYPE_5 embedded, TYPE_8 embedded, separate SDS value, stringRef) — no zmalloc calls
• Wired hashEntryGetSize callback into hashHashtableType and hashWithVolatileItemsHashtableType
• 3 in-place mutation sites in t_hash.c need manual delta tracking via hashtableAdjustTrackedDataBytes():
  • entryUpdate in hashTypeSet (value change)
  • entryUpdateAsStringRef in hashTypeUpdateAsStringRef (stringRef path)
  • entrySetExpiry in hashTypeSetExpire and hashTypePersist (expiry toggle)

Design

• Logical size, not allocation size: tracks semantic sizes from struct fields, never calls zmalloc_size
• Data separated from metadata: tracked_data_bytes = sum of entry logical sizes. Metadata = hashtableMemUsage() (struct + buckets), computed O(1) from existing fields

Tests

• test_set_tracking.cpp — 22 tests covering all mutation paths + 2 non-deterministic fuzzers
• test_hash_tracking.cpp — 17 tests covering all mutation paths including expiry toggle, stringRef, conversion, and a non-deterministic fuzzer