fix(devserver): warn instead of silently dropping duplicate eval_name (#366)

[srijanarya]

What

create_app built the evaluator registry with a dict comprehension:

_all_evaluators = {evaluator.eval_name: evaluator for evaluator in evaluators}

When two Eval(...) share an eval_name, the later one silently overwrites the earlier. The dev server starts fine, but GET /list returns only one of them — and the startup log (Loaded N evaluator(s)) counts the pre-dedup list, so it disagrees with what's actually served. An entire eval is dropped with no signal. This is the behavior reported in #366.

Change

Build the registry explicitly instead:

• Warn, don't drop — emit a UserWarning naming the duplicated eval_name, so the conflict is visible at load time.
• First wins — keep the first registration and skip the duplicate, mirroring how duplicate reporters are handled in cli/eval.py.
• Honest count — report len(_all_evaluators) after create_app runs, so the startup log matches exactly what /list serves.

Test

Adds test_create_app_warns_and_keeps_first_on_duplicate_eval_name: asserts the UserWarning fires, the first evaluator is the one kept, and exactly one entry remains. Skips cleanly when the devserver extras aren't installed.

1 passed, 9 deselected

Closes #366.