Change addConsLocal(), addConsNode() to accept ExprCons

[Joao-Dionisio]

There were a bunch of issues and PRs related to addConsNode() not behaving as expected (#391, #580, #605), and the current implementation forces users to use an event handler whenever they want to implement a slightly more complicated branching decision. In this event handler, they then use addConsLocal()

This is a breaking change, but I feel like it should be done.
A middle ground would be to accept both ExprCons and Constraint, but it doesn't feel very elegant. addCons() doesn't do this. Any thoughts, @mmghannam ?

[Copilot]

Pull request overview

This PR changes addConsNode() and addConsLocal() to accept ExprCons instead of Constraint, aligning their API with addCons() and addressing issues from previous PRs (#391, #580, #605). The functions now also return the created Constraint object for user reference.

Changes:

• Modified addConsNode() and addConsLocal() to accept ExprCons expressions instead of Constraint objects
• Added return values to both functions, returning the created Constraint object
• Added comprehensive test coverage in a new test file test_addconsnode.py

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/pyscipopt/scip.pxi	Refactored addConsNode() and addConsLocal() to accept ExprCons, follow the addCons pattern for constraint creation, and return Constraint objects
tests/test_addconsnode.py	Added new comprehensive tests for both addConsNode and addConsLocal with custom branching rules
CHANGELOG.md	Documented the breaking change in the Changed section

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