Copybara import of the project:
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c1d0d649b5aae1322a02dbaa586822d69b8546f6 by allengour <allengour@google.com>:
fix: fix and test `config.after_timestamp` behavior in `InMemorySessionService.get_session()`
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/438 from allengour:fix/issue-437-after_timestamp-behavior 4b49a5e6509b5ad9dd9103a6dc357fd44c101f31
PiperOrigin-RevId: 755492201