#817 Don't confuse tables where one name is a prefix of the other

[pgarrison]

Context

Resolves #817

Changes

To work around the underlying bug, register files to duck DB with an appended -bff-filehandle. Unfortunately, this means updating every place where the SQL references the file handle name to use the new fileHandleName function. It's a little tricky to ensure all of these sites were identified: I missed the ones in parquetHasBlankValues at first. I suspect all of the sites that need to change are in the data source preparation phase, because subsequent queries use view/table names instead.

Testing

Three manual tests:

1. Two parquet files tiny.parquet and tiny2.parquet and verify both appear as distinct data sources with correct row counts.
2. parquet_metadata: Load a single parquet file with a column containing blank/whitespace values and confirm the column filter UI correctly identifies blanks.
3. Non-parquet: Load a CSV and a JSON to verify they still load and aggregate as normal.