[common][python] Support SUBSTRING and TRIM in column masking

[plusplusjiajia]

Purpose

SubstringTransform and TrimTransform are not listed in Transform's @JsonSubTypes, so Jackson writes the class simple name as the type id and reading it back fails with InvalidTypeIdException. Both are therefore unusable for column masking, where a rule is stored as JSON and replayed later — the only usable masks today are NULL and CONCAT of a constant, so keeping the last four characters of a value cannot be expressed.

Registering them needs three more things:

• SubstringTransform had no Jackson annotations, so its inputs were dropped. It gets a @JsonCreator and a deserializer extending StringTransform's with a number branch, since its positions may be integers.
• TrimTransform's trimFlag was not serialized, and name() returns TRIM for all three flags, so LTRIM/RTRIM would silently degrade into TRIM. It becomes its own property, and part of equals/hashCode.
• pypaimon executes the same rules and raised Unknown transform type for both. It gains them, following the Java semantics rather than the nearest Arrow kernel — a one-input TRIM trims spaces only, and its character argument is a set.