[common] Reject out-of-range integral casts when extracting a variant scalar

[zhuxiangyi]

Purpose

This is a bug fix. Extracting a variant number into a narrower integral type returns a wrong number instead of NULL/an error when the value does not fit.

The cast goes through the generic CastExecutors rules (Number::intValue, (int) DecimalUtils.castToIntegral(...)), which wrap or saturate an out-of-range value. With spark.sql.variant.pushVariantIntoScan=true on Spark 4.1 the cast runs inside the Paimon reader, so the same query returns different numbers depending on the session flag:

CREATE TABLE T (id INT, v VARIANT);
INSERT INTO T VALUES (1, parse_json('{"n":99999999999,"d":1e30}')), (2, parse_json('{"n":7,"d":1.5}'));

SELECT id, try_variant_get(v, '$.n', 'int'), try_variant_get(v, '$.d', 'bigint') FROM T ORDER BY id;
-- pushVariantIntoScan=true : (1, 1215752191, 9223372036854775807), (2, 7, 1)   <- wrong
-- pushVariantIntoScan=false: (1, NULL, NULL), (2, 7, 1)                        <- Spark's TRY cast

The shredded typed_value path (BaseVariantReader.ScalarReader) has the same problem through the same cast rules, e.g. a BIGINT typed value read as INT.

This PR checks the truncated value against the target range before delegating to the cast rules, in a helper shared by VariantGet and the scalar reader, so an out-of-range number becomes an invalid cast (NULL for try_variant_get, an error for variant_get), matching Spark. A cast rule returning null (e.g. a BIGINT that overflows a DECIMAL(p, s) target) is now also reported as an invalid cast instead of being returned as a silent NULL under failOnError=true.

In-range behaviour is unchanged: fractional parts are still truncated (1.5 as int → 1) and widening casts still succeed.

Tests

The new tests reproduce the bug: on master they fail with expected: null but was: 1215752191, and pass with this change.

• GenericVariantTest#testVariantGetIntegralOverflow: LONG / DOUBLE / DECIMAL inputs into TINYINT..BIGINT, try mode returns NULL, strict mode throws; boundary values still cast.
• VariantShreddingReadTest#testReadIntegralOverflowAsInvalidCast: parameterised over a plain file and a file shredded with n BIGINT, d DOUBLE, covering both VariantGet and the shredded scalar reader.
• VariantTestBase: try_variant_get out-of-range extraction returns NULL; runs under all four Spark 4.x configurations (with/without pushdown, with/without inferred shredding). Verified on Spark 4.1.2: 116 tests pass.

API and Format

No.

Documentation

No.