refactor(common): centralize checked class-pointer casts

[lxy-9602]

Purpose

Introduce Paimon-owned checked_cast and checked_pointer_cast helpers that delegate to Arrow's debug-checked cast implementation.

This change:

• Replaces direct uses of arrow::internal::checked_cast and arrow::internal::checked_pointer_cast.
• Replaces class-hierarchy static_cast and std::static_pointer_cast usages with the Paimon helpers where applicable.
• Validates null pointers and Arrow type IDs before checked casts when a type mismatch is a recoverable runtime error.
• Keeps dynamic_cast when cast failure represents an expected runtime branch or is handled by an existing null-check macro.
• Keeps discriminator-guarded std::static_pointer_cast for non-polymorphic hierarchies such as parquet::Page.
• Documents the checked-cast conventions and exceptions in the code style guide.

Tests

API and Format

Documentation

Updated docs/code-style.md.

Generative AI tooling

Generated-by: OpenAI Codex (GPT-5)

[lszskye]

no assert here?