upgrade python and added unittests

[mukeshbhatt18gl]

Description of change

This PR upgrades the project’s Python runtime/dependency baseline and introduces a new unittest-based test suite to validate discovery, sync behavior, bookmarks/start-date handling, pagination, and field-selection rules.

SAC-28706

Manual QA steps

Risks

Rollback steps

• revert this branch

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[Copilot]

Pull request overview

This PR upgrades the project’s Python runtime/dependency baseline and introduces a new unittest-based test suite to validate discovery, sync behavior, bookmarks/start-date handling, pagination, and field-selection rules.

Changes:

• Upgrade CI virtualenv Python version to 3.12 and add CI steps to run unit + broader test discovery.
• Bump core dependency pins (backoff/requests/pendulum/singer-python).
• Add a set of unit tests under tests/unittests/ plus additional tests under tests/ covering sync/discovery/state behaviors.

Reviewed changes

Copilot reviewed 14 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/unittests/test_sync_selection_unit.py	Unit tests for stream selection/custom stream detection and export-row transformation.
tests/unittests/test_sync_helpers_unit.py	Unit tests for retry interval logic and bookmark helpers.
tests/unittests/test_schema_unit.py	Unit tests for schema helpers (naming, pk selection, field typing).
tests/unittests/test_discover_unit.py	Unit tests for discovery metadata/keys behavior via patched schema sources.
tests/test_sync.py	Higher-level sync tests with mocked client + Singer output functions.
tests/test_start_date.py	Tests for start-date vs bookmark precedence for static + bulk sync paths.
tests/test_pagination.py	Tests static endpoint pagination behavior and bookmark writing.
tests/test_discovery_metadata.py	Tests forced replication method metadata for known streams.
tests/test_discovery_enhanced.py	Broader discovery tests validating catalog structure/metadata/schemas.
tests/test_bookmark.py	Tests bookmark writers + static sync bookmark usage.
tests/test_automatic_fields.py	Tests that automatic fields are exported even if unselected.
tests/test_all_fields.py	Tests selected-field export behavior and 250-field limit enforcement.
tests/base.py	Shared base test utilities/expected metadata.
setup.py	Updates pinned dependency versions.
.circleci/config.yml	Switch CI to Python 3.12, update schema validation path, add unittest execution steps.

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[RushiT0122]

This not required anymore since we moved this condition above. You may also need to update the elif conditions

[RushiT0122]

Ideally this tap side change doesn't fall into scope of this PR, also we don't have test account to test it thoroughly, therefore I would not mind if we remove these changes to avoid any disruption on the prod connections.

[mukeshbhatt18gl]

Removed out of scope changes

[RushiT0122]

Suggested change

	"""Convert a date string or pendulum DateTime to the format expected by Eloqua
	API filter expressions (``YYYY-MM-DD HH:MM:SS``).
	Using an explicit ``.format()`` call instead of the deprecated
	``.to_datetime_string()`` guards against Pendulum 2→3 behavioural differences.
	"""
	"""Convert a date string or pendulum DateTime to the format expected by Eloqua
	API filter expressions (``YYYY-MM-DD HH:MM:SS``).
	"""

[RushiT0122]

Also I observed that .to_datetime_string() still works

[mukeshbhatt18gl]

roll back the change.