feat(go): add filter push-down and predicate API for Go binding

[luoyuxia]

Purpose

Add filter push-down and predicate API support to the Go binding, enabling Go callers to filter table scans with native Go values.

Linked issue: close #214

Brief change log

• [bindings/c/src/types.rs] Add paimon_predicate, paimon_datum (tagged flat struct with Timestamp/Decimal/Bytes fields), ReadBuilderState.filter, TableScanState
• [bindings/c/src/result.rs] Add paimon_result_predicate
• [bindings/c/src/table.rs] Add 10 leaf predicate functions, 3 combinators (and/or/not), with_filter, fix scan to propagate filters via TableScanState; add integer datum auto-coercion across integer-family types; fix empty string datum handling
• [bindings/go/predicate.go] PredicateBuilder type with short methods (Eq, NotEq, Lt, Le, Gt, Ge, IsNull, IsNotNull, In, NotIn); Predicate.And/Or/Not combinator methods (return errors, no panics); Go value types (Date, Time, Timestamp, LocalZonedTimestamp, Decimal with full i128, Bytes); automatic type inference from Go literals; FFI wrappers
• [bindings/go/predicate/predicate.go] New sub-package with variadic And/Or convenience functions and Not wrapper
• [bindings/go/read_builder.go] Add ReadBuilder.WithFilter method (nil-safe, no-op)
• [bindings/go/table.go] Add Table.PredicateBuilder() factory method
• [bindings/go/types.go] Add Go mirror types for datum/predicate FFI structs
• [bindings/go/tests/paimon_test.go] Add TestReadWithFilter with subtests, refactor shared test helpers

Tests

• TestReadWithFilter/EqualById: filters id = 1, verifies 1 matching row
• TestReadWithFilter/EmptyStringEqual: verifies Eq("name", "") is accepted and returns 0 rows
• Refactored existing tests to use shared openTestTable and readRows helpers

API and Format

Go API usage:

import pred "github.com/apache/paimon-rust/bindings/go/predicate"

// Create a predicate builder from a table
pb := table.PredicateBuilder()

// Native Go literals — type auto-inferred
idEq, _ := pb.Eq("id", 1)
nameEq, _ := pb.Eq("name", "alice")

// Dedicated types for temporal/special types
datePred, _ := pb.Eq("dt", paimon.Date(19000))
tsPred, _ := pb.Eq("ts", paimon.Timestamp{Millis: 1700000000000, Nanos: 0})
decPred, _ := pb.Eq("amount", paimon.NewDecimal(12345, 10, 2))

// IN predicate with variadic args
inPred, _ := pb.In("id", 1, 2, 3)

// Combinator methods on Predicate
combined, _ := idEq.And(nameEq)
combined, _ := idEq.Or(nameEq)
negated, _ := idEq.Not()

// Variadic convenience functions (sub-package)
filter, _ := pred.And(pred1, pred2, pred3)
filter, _ := pred.Or(pred1, pred2)
negated, _ := pred.Not(pred1)

// Apply filter
rb.WithFilter(filter)

Documentation

N/A

[JingsongLi]

Can you create a documentation for Go API?