fix: resolve schema mismatch between hot and cold memory paths

[yaowubarbara]

Summary

• Fixes Schema mismatch between create_manage_memory_tool and create_memory_store_manager #138: MemoryStoreManager crashes with KeyError: 'kind' when reading memories written by create_manage_memory_tool
• Fixes create_search_memory_tool does not retrieve memories written via create_memory_store_manager #140: create_search_memory_tool returns nested/inconsistent format for memories written by MemoryStoreManager

Problem

The two memory write paths use incompatible value schemas:

Path	Writes
create_manage_memory_tool (hot)	{"content": <str_or_dict>}
MemoryStoreManager (cold)	{"kind": "Memory", "content": {...}}

When both paths coexist (which is the recommended pattern per docs), the cold path crashes on item.value["kind"] because the hot path never writes a kind key.

Solution

Backward-compatible read-side fix — no changes to write formats, no breaking changes.

• _parse_store_value() in extraction.py: Normalizes both formats into a (kind, content) tuple. If kind is missing, defaults to "Memory" and wraps bare strings into the expected dict format.
• _normalize_memory_value() in tools.py: Unwraps the kind/content envelope in search results so the LLM always sees a consistent, flat value regardless of which code path wrote the memory.

Both helpers are used in all 4 affected code locations (2 in ainvoke, 2 in invoke).

Tests

Added 13 unit tests in tests/test_schema_compat.py covering:

• Cold path format (with and without custom schemas)
• Hot path format (string content, dict content, numeric edge case)
• Edge cases (empty dict, unknown keys, partial envelope)
• Normalization passthrough for non-dict values