fix: lazy-load auth deps in web/Pyodide startup and add regression tests

[ndonkoHenri]

Fix #6258

Summary by Sourcery

Lazy-load optional authentication dependencies to avoid import-time failures when auth is unused and add regression tests to validate this behavior.

New Features:

• Introduce lazy attribute resolution in the flet.auth package so auth service and provider classes are loaded on first access rather than at module import time.

Bug Fixes:

• Prevent failures when importing flet or flet.auth in environments where optional auth dependencies (httpx, oauthlib) are not installed by deferring their imports until actually needed.

Enhancements:

• Adjust authorization service internals to work with lazily imported dependencies while keeping the public API unchanged.

Tests:

• Add regression tests ensuring flet imports successfully without optional auth dependencies, auth exports remain accessible, and oauthlib is only required when authorization logic is invoked.

[sourcery-ai]

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[Copilot]

Pull request overview

Fixes a Pyodide/web startup crash caused by eager imports of optional auth dependencies (httpx, oauthlib) by deferring those imports until the relevant auth code paths are actually used.

Changes:

• Made httpx imports lazy in GitHubOAuthProvider user/group fetching.
• Made httpx/oauthlib imports lazy in AuthorizationService (and adjusted typing to avoid oauthlib types at import-time).
• Added regression tests ensuring import flet / import flet.auth succeed when httpx and oauthlib are unavailable.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
sdk/python/packages/flet/tests/test_auth_lazy_imports.py	Adds regression tests that simulate missing optional auth deps and validate lazy-import behavior.
sdk/python/packages/flet/src/flet/auth/providers/github_oauth_provider.py	Moves httpx import into the async fetch methods to avoid import-time dependency.
sdk/python/packages/flet/src/flet/auth/authorization_service.py	Defers httpx/oauthlib imports to call sites and removes oauthlib type imports from module import-time.
sdk/python/packages/flet/src/flet/auth/init.py	Lazily exposes auth exports via module __getattr__ to avoid eager importing of auth implementation/provider modules.

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