fix(python-sdk): log direct experiment URL from evaluate() (#7462)

[aiedwardyi]

Closes #7462.

evaluate() logged an opaque v1/session/redirect/experiments/... URL that breaks in offline / air-gapped environments. This mirrors the dataset fix (#7440) and builds the direct frontend URL instead:

{domain_root}opik/{workspace}/experiments/{dataset_id}/compare?experiments=[...]

• get_experiment_url_by_id now takes base_url, workspace and returns the direct URL, matching get_dataset_url_by_id / get_test_suite_url_by_id.
• Updated the 5 call sites in evaluator.py to pass workspace=client._dereferenced_workspace(). This resolves the default-workspace sentinel, matching how the dataset/project URLs are built - passing raw _workspace would produce a broken link on default workspaces.
• Added a parametrized unit test mirroring the existing dataset / test-suite cases.

Review fixes applied: 1b7a43d - wrapped the new url-helper lines to the 88-char limit (Baz review).

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