fix(plugin-parquet): NUMBER exports as BIGINT and PostgreSQL money as null

[datlechin]

Summary

• Oracle, Snowflake and Dameng NUMBER columns exported to Parquet as BIGINT, so every fraction was rounded and values past 2^63 became null. Root cause: number sat in the mapper's integer family, and the base-name match drops the declared (p,s).
• DECIMAL(p,s) and NUMERIC(p,s) columns exported as DOUBLE, losing digits past about 15 significant ones. Root cause: the mapper ignored the declared precision and scale for the whole exact-numeric family. A declaration now maps to DECIMAL(p,s), or to BIGINT for scale 0 with at most 18 digits. A missing declaration, *, or more than 38 digits stays DOUBLE. SQLite, libSQL, Turso and Cloudflare D1 also keep DOUBLE, because they keep a value such as 19.9875 in a DECIMAL(10,2) column as a plain float and never enforce the scale.
• Oracle BINARY_FLOAT and BINARY_DOUBLE columns exported as text. Root cause: neither type name was in any numeric family.
• PostgreSQL money values written as null. Root cause: money mapped to DOUBLE, but PostgreSQL sends it as locale text such as $1,234.56, and TRY_CAST turns that into null. PostgreSQL money now stays text. SQL Server money and smallmoney, which arrive as plain decimal text, map to DECIMAL(19,4) and DECIMAL(10,4).
• Stopping a multi-table Parquet export between tables left the files already written. Root cause: the loop-head cancellation check sat outside the do/catch that removes those files.

Tests

• ParquetTypeMapperTests.declaredExactNumericKeepsPrecision: fails without the fix. NUMBER(19) came back BIGINT on main and DOUBLE on the first version of this branch, where it should be DECIMAL(19,0).
• ParquetTypeMapperTests.undeclaredExactNumericIsDouble: fails without the fix, because bare NUMBER mapped to BIGINT.
• ParquetTypeMapperTests.exactNumericWithScaleZeroIsAnInteger: fails without the fix, because DECIMAL(10,0) and numeric(5) mapped to DOUBLE.
• ParquetTypeMapperTests.sqliteFamilyIgnoresDeclaredPrecision: fails on main (number(19) mapped to BIGINT). It also failed on this branch until the SQLite-family check was added.
• ParquetTypeMapperTests.oracleBinaryFloatsAreDoubles: fails without the fix, because both types mapped to VARCHAR.
• ParquetTypeMapperTests.postgresMoneyStaysText and sqlServerMoneyIsFixedPoint: both fail without the fix, because money mapped to DOUBLE on every engine.
• ParquetTypeMapperTests.doubleFamilies: spec change. money and DECIMAL(10,2) leave the list of types pinned to DOUBLE.
• ParquetExportCancellationTests.stopBetweenTablesRemovesWrittenFiles: fails when the cancellation check sits outside the cleanup. The other three cases pin paths that already worked: a failing table removes earlier files, a finished export keeps every file, and a single table writes to the destination itself.

Docs

User-facing text is covered by the docs rewrite branch.