Expose lp basis methods

[Joao-Dionisio]

Fix #1195

[Copilot]

Pull request overview

This PR addresses issue #1195 by exposing LP basis information in the Python LP API, including an enum for basis statuses and a regression test to ensure basis round-tripping works.

Changes:

• Added LP.getBase() / LP.setBase() for retrieving and restoring column/row basis statuses via SCIP’s LPI.
• Exposed basis status constants as SCIP_BASESTAT from the package.
• Added a test exercising basis get/set and verifying basis preservation after re-solve.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/pyscipopt/lp.pxi	Implements LP.getBase() / LP.setBase() using SCIPlpiGetBase / SCIPlpiSetBase.
src/pyscipopt/scip.pxd	Adds C declarations for SCIPlpiGetBase / SCIPlpiSetBase.
src/pyscipopt/scip.pxi	Exposes PY_SCIP_BASESTAT mapping to SCIP base status constants.
src/pyscipopt/scip.pyi	Updates typing stubs to include LP.getBase, LP.setBase, and PY_SCIP_BASESTAT.
src/pyscipopt/__init__.py	Re-exports PY_SCIP_BASESTAT as SCIP_BASESTAT.
tests/test_lp.py	Adds basis get/set test coverage for the LP class.
CHANGELOG.md	Documents the newly added LP basis APIs.

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