Reuse a runtime-descriptor LTO driver for multi-output AST JIT

[vyasr]

Description

AST (expression-tree) JIT evaluation currently compiles generated expression code together with the transform driver that traverses rows and handles inputs and outputs. Changing the expression or its types can therefore require recompiling driver code as well, even though the row traversal is largely reusable.

This PR separates compatible multi-output evaluations into two compiled fragments: the generated expression operation and a schema-independent driver. LTO (link-time optimization) links those fragments into an executable GPU kernel. The driver receives runtime descriptors containing column pointers, null masks, offsets, and scalar information rather than specializing its interface for each input/output schema. This allows its compiled fragment to be reused across different expressions and supported schemas.

• Use the new path for BOOL8, integer, and floating-point inputs/outputs. Keep source JIT for single-output evaluation and unsupported representations, including decimals and temporal types, whose logical semantics need more than the supported storage-type interface.
• Pack aligned input/output descriptors into one asynchronous transfer, using the current memory resource for scratch storage.
• Cache linked kernels by generated source, embedded bundle, CUDA runtime/driver, target SM, and LTO architecture. Resolve fragments only on a linked-library miss, avoiding that work when the executable kernel is already cached.
• Preserve expression lowering through Row IR, result ordering, null/error semantics, output allocation, and RTCX cache behavior without changing public APIs.
• Add focused coverage for per-type overflow errors, nullable grid-stride execution and partial warps, linked-kernel cache identity, sliced inputs, scalars, and empty inputs. Existing arithmetic and decimal tests continue to cover ordinary/NULLIFY results and source-JIT fallback.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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[vyasr]

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