fix: replace console.warn() with debug library in concerto-core

[23harshitkumar]

Fixes: N/A

Summary:

Replace remaining console.warn() calls with the debug library in concerto-core, following the same pattern established in #1125 (HTTPFileLoader).

Changes:

• basemodelmanager.js : Replace console.warn for invalid metamodel warnings with debug('concerto:BaseModelManager') (already imported)

• jsonpopulator.js : Add debug('concerto:JSONPopulator') import and replace console.warn for TZ environment variable warnings

• modelmanager.js (test) : Update comment to reflect new behavior.

Why these changes:

console.warn() pollutes console output in production environments, CI pipelines, etc. The debug library allows users to opt-in to these warnings via DEBUG=concerto:* when needed.

Testing:

• All 149 tests pass (modelmanager.js + jsonpopulator.js).

[23harshitkumar]

@ekarademir @mttrbrts the PR is ready for a review!

[mttrbrts]

I like the change, but let's target this to v4.0.0?

[23harshitkumar]

@mttrbrts I have a question for this repo. Am I supposed to focus all my new PRs to the v4.0.0 branch?
Is this because we're primarily working and focusing on the v4.0.0 for now?

[23harshitkumar]

@mttrbrts I changed the base branch from main to v4!

Conflicts resolved and rebased onto v4.0.0! Tests pass locally, but I see CI is failing. Is this expected for the v4.0.0 branch or should I investigate further?