feat: CG-10779: Global session management + decoupled auth

[caroljung-cg]

Changes

• Decouples auth from codegen session
• Create a global session manager for headless compute

Content

Testing

Please check the following before marking your PR as ready for review

• I have added tests for my changes
• I have updated the documentation or added new documentation as needed

[codecov]

❌ 2 Tests Failed:

Tests completed	Failed	Passed	Skipped
30	2	28	0

View the top 2 failed test(s) by shortest run time

::tests.unit.codegen.sdk.core.test_directory

Stack Traces | 0s run time

ImportError while importing test module '.../sdk/core/test_directory.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
.../sdk/core/test_directory.py:8: in <module>
    from codegen.sdk.codebase.codebase_graph import CodebaseGraph
E   ModuleNotFoundError: No module named 'codegen.sdk.codebase.codebase_graph'

::tests.unit.codegen.shared.configs.test_constants

Stack Traces | 0s run time

ImportError while importing test module '.../shared/configs/test_constants.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
.../shared/configs/test_constants.py:3: in <module>
    from codegen.shared.configs.constants import (
E   ImportError: cannot import name 'ENV_FILENAME' from 'codegen.shared.configs.constants' (.../shared/configs/constants.py)

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[github-actions]

🎉 This PR is included in version 0.11.0 🎉

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