fix(loaders): honor interval in local loader by resampling

[Shizoqua]

The local loader accepted an interval argument but passed it only to the cache key, so requesting e.g. 4H against hourly data silently returned the file's native bars.

Changes

• Resample to the requested interval using standard OHLCV aggregation (open=first, high=max, low=min, close=last, volume=sum)
• Warn when a finer-than-source interval is requested (cannot fabricate bars)
• Warn on unsupported interval strings
• Make end-date filter inclusive of the whole end day so intraday bars on the final date survive for sub-daily intervals
• Bump loader cache version (2→3) so the end-date and resampling fixes cannot be masked by stale cache entries

Testing

• Test verifies 4H request against hourly bars produces correct aggregated buckets
• Test verifies upsampling returns source bars with a warning

[warren618]

Merged — thanks. The cache-version bump so stale entries can't mask the fix is exactly right, and the inclusive end-day filter closes the sub-daily edge case. Verified locally: local-loader + cache helper tests green.