feat: fall back to bundled data.json when remote URL returns non-200

[Aryan-Shastri]

Problem

Users on older installations (e.g. Ubuntu 24.04 apt package shipping sherlock 0.14.3) hit a cryptic crash when the remote MANIFEST_URL returns a non-200 response:

Bad response while accessing data file URL 'https://...'

No fallback, no actionable guidance — just a hard failure.

Fix

When the remote data URL returns a non-200 response, fall back to the bundled sherlock_project/resources/data.json that ships with the package, and print a warning so the user knows what happened.

If the local fallback also doesn't exist, raise a FileNotFoundError with an actionable message (pip install -U sherlock-project) instead of a bare crash.

Behaviour after this change

• Remote fetch succeeds → no change, works as before
• Remote fetch returns non-200 → falls back to local data.json, prints warning
• Local fallback missing too → clear error with upgrade instructions

Testing

# Simulate the broken old URL from #2924
from sherlock_project.sites import SitesInformation
s = SitesInformation('https://raw.githubusercontent.com/sherlock-project/sherlock/master/sherlock/resources/data.json')
# Output: Warning: Remote data unavailable (HTTP 404). Falling back to bundled local data file.
# Output: Loaded 440 sites from fallback
Closes #2924



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