Python: Add FileMemoryProvider context provider sample

[westey-m]

Motivation & Context

FileMemoryProvider gives an agent file-based memory through the file_memory_* tools, with each memory stored in an AgentFileStore.

Until now, Python did not have a focused sample showing how to attach the provider directly to an Agent, persist memories on disk, or configure a stable scope so memories can be recalled across independent sessions.

This adds the Python counterpart to the .NET sample in #7401, alongside the other context-provider samples.

Description & Review Guide

• What are the major changes?
  • Add file_memory_provider.py, a Foundry-backed travel assistant using FileMemoryProvider over FileSystemAgentFileStore.
  • Demonstrate a stable per-user scope, one session that stores user preferences, the resulting files on disk, and a new session that recalls those preferences without shared chat history.
  • Document the sample and its prerequisites in the context-provider README.
• What is the impact of these changes?
  • Samples-only and additive; no framework APIs or runtime behavior change.
• What do you want reviewers to focus on?
  • Whether the stable per-user scope and two-session flow clearly explain the distinction between Python's default per-session isolation and explicit cross-session memory sharing.

Related Issue

Related to #6448.

Issue #6448 tracks several additional harness samples, so this PR contributes the Python FileMemoryProvider sample without closing the broader issue. PR #7401 is the complementary .NET sample; this PR adds the Python implementation under 02-agents/context_providers and demonstrates Python's scope API.

Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
• The PR follows the Contribution Guidelines
• This PR is linked to an issue and there is no other open PR for this issue (see Related Issue above).
• This is not a breaking change. If it is a breaking change, add the breaking change label (or add "[BREAKING]" to the title prefix, before or after a language prefix) — a workflow keeps the label and title prefix in sync automatically.

[Copilot]

Pull request overview

Adds a focused Python sample demonstrating FileMemoryProvider + FileSystemAgentFileStore to persist “memory files” on disk and recall them across independent AgentSessions using a stable per-user scope, and documents it alongside the other context-provider samples.

Changes:

• Add a new Foundry-backed sample (file_memory_provider.py) showing file-based memory persistence across two separate sessions via an explicit scope.
• Update the context-provider samples README to include the new sample and list its prerequisites.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
python/samples/02-agents/context_providers/README.md	Registers the new sample in the samples list and documents required env vars/auth.
python/samples/02-agents/context_providers/file_memory_provider.py	New end-to-end sample wiring FileMemoryProvider over FileSystemAgentFileStore and demonstrating cross-session recall via stable scope.

[github-actions]

Automated Code Review

Reviewers: 4 | Confidence: 43% | Result: All clear

Reviewed: Security Reliability, Test Coverage, Failure Modes, Design Approach

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Automated review by westey-m's agents

[github-actions]

Automated Code Review

Reviewers: 5 | Confidence: 52% | Result: All clear

Reviewed: Correctness, Security Reliability, Test Coverage, Failure Modes, Design Approach

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Automated review by westey-m's agents