refactor(memory): convert memory classes to serializable

[greysonlalonde]

Note

Medium Risk
Refactors core memory types (Memory, MemoryScope, MemorySlice) to Pydantic BaseModel, which can subtly change initialization/attribute semantics and impacts any code relying on the previous private _read_only flag or direct patching of instance methods.

Overview
Memory refactor for serialization: Memory, MemoryScope, and MemorySlice are converted to Pydantic BaseModels with fields + model_post_init/validators to set up runtime-only dependencies (LLM/embedder/storage) while keeping instances serializable.

API/behavior adjustments: replaces the private _read_only flag with a public read_only boolean (and MemoryScope.read_only passthrough), tightens depth typing to Literal["shallow", "deep"], and updates remember/tooling to no-op consistently when read_only=True.

Integration/test updates: agent memory save paths (CrewAgentExecutorMixin, LiteAgent, create_memory_tools) now check memory.read_only, and tests patch Memory methods at the class level to avoid Pydantic instance attribute restrictions while updating constructors to keyword-based MemoryScope(memory=..., root_path=...) / MemorySlice(memory=..., scopes=...).

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