196 station status or vehicle status should be required

[jcpitre]

Summary

Fixes #196 — A GBFS feed must be dock-based, free-floating, or hybrid, meaning at least one of station_status / vehicle_status (v3+) or station_status / free_bike_status (pre-v3) must be present. Previously, the validator accepted feeds with neither file without reporting any error.

Changes

• GbfsJsonValidator: Added a post-validation check (checkStatusFilePresence) that flags both status files as conditionally required — with 1 error each — when neither is present in the feed.
• FileValidationResult: Added a conditionallyRequired field to distinguish between files that are always required by the spec and files that are required only when a counterpart is absent.
• ConsoleReportFormatter: Updated to display [CONDITIONALLY REQUIRED] instead of [REQUIRED] for these files.
• Tests: Added 4 new test cases covering v3 and pre-v3 feeds for both the missing-both and missing-one scenarios. Updated existing tests to account for the new rule.
• Example: Updated GbfsValidatorExample to use Loader for feed discovery.

Example

Running against https://opendata.agglo-larochelle.fr/sites/default/files/dataset/2dc/df9ac-ca89-4e3f-af7e-5d75f255ee5e/gbfs.json (the feed mentioned in #196) now produces:

⚠ station_status [CONDITIONALLY REQUIRED] - NOT FOUND
⚠ vehicle_status [CONDITIONALLY REQUIRED] - NOT FOUND
Result: INVALID

[davidgamez]

LGTM!

[testower]

I should have noticed this sooner. This is a redundant check since we already validate this on the gbfs.json schema. The only thing that this PR adds is a check that they are reachable on the network. IMHO this adds unnecessary complexity for something that could fail for other reasons. I believe we discussed this on the tools contributor meeting.

[jcpitre]

@testower we won't release until this is settled (or thrown out)