[common] Fix JSON round-trip of temporal and decimal predicate literals - #9640

Purpose

close #9639

LeafPredicate handed its literals to Jackson as whatever PredicateBuilder.convertToJavaObject produced. JsonSerdeUtil registers JavaTimeModule without disabling WRITE_DATES_AS_TIMESTAMPS, so a LocalDate was written as [2026,1,15] and a BigDecimal as a JSON number; reading those back yields an ArrayList and a Double, and PredicateBuilder.convertJavaObject rejects both. DATE, TIME, TIMESTAMP, TIMESTAMP_LTZ and DECIMAL literals therefore could not round-trip at all: the writer's output is exactly what the reader refuses.

Those five now go out as strings, ISO-8601 for the temporal types and toPlainString for decimals, and come back through the matching parse before convertJavaObject sees them. Everything else is untouched.

This changes the wire representation of those five literals. For Paimon's own Java reader nothing that worked before breaks, because reading these literals back never worked: the writer emitted exactly what the reader refused. A REST server that parses the filter JSON with its own implementation is a separate case. Where it used to see an array or a number it now sees a string, and I have no evidence about how any given server handled the old forms. So the rollout order matters: the server has to understand the new string encoding before an upgraded client emits it. Deploy the server-side parser first, and call the encoding change out in the release notes.

The reader deliberately does not also accept the old array and number forms. I had that in an earlier version and dropped it: Paimon's reader never accepted those shapes, so there is no stored or in-flight predicate in that form that used to work, and reconstructing them means guessing at things like which trailing fields Jackson omitted and how much precision a double kept. If a concrete compatibility case turns up, that is worth adding on its own terms.

Tests

PredicateJsonSerdeTest.testTemporalAndDecimalLiteralsRoundTrip builds a predicate over a row with all five affected types, including a DECIMAL(20,3) with more significant digits than a double can hold, serializes it and asserts the parsed predicate equals the original.

RESTApiJsonTest covers the same five literals inside the actual ListPartitionsByFilterRequest envelope, so the REST request that carries a partition filter round-trips end to end.

Against the unfixed code the round-trip test fails with UnsupportedOperationException: Unexpected date literal of class java.util.ArrayList.

mvn -pl paimon-common -Dtest=PredicateJsonSerdeTest test on JDK 8: 91 tests, 0 failures. spotless:check and checkstyle:check on paimon-common are clean.