Add Mem0 integration / Support memory in Agent

[Amnah199]

Related Issues

• partially fixes - #219

Proposed Changes:

• This PR integrates mem0 as a memory store in Haystack, supporting basic add, retrieve, and delete operations.
• It updates the memory_agents.Agent class to enable retrieving and persisting long-term conversational context.

Key Changes

• Added memory support to memory_agents.Agent.
• Before each execution, relevant memories are fetched from Mem0MemoryStore using the latest user message as the query.
• Retrieved memories are injected into the conversation as [MEMORY #n] ChatMessage objects.
• When memories exist, the system prompt is updated to tell the LLM that [MEMORY] messages represent long-term context.
• After each run, new user and assistant messages are saved to the memory store.
• Memory is optional; agents behave normally when memory_store=None.

How did you test it?

• Unit and Integration Tests
• Tested locally with examples

Notes for the reviewer

Support for Memory.from_config will be revised in a separate PR as it has a slightly different implementation than mem0 MemoryClient.
https://docs.mem0.ai/platform/platform-vs-oss

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 20066169239

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 94 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-2.2%) to 71.082%

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Files with Coverage Reduction	New Missed Lines	%
components/agents/agent.py	94	53.88%

Totals
Change from base Build 20012634360:	-2.2%
Covered Lines:	1288
Relevant Lines:	1812

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💛 - Coveralls