Add Filter v2 capability metadata

[rustyconover]

Summary

• model all Filter-v2 FunctionInfo capability fields in the C++ SDK
• advertise vgi.duckdb.standard.v1 by default for functions that enable filter pushdown
• serialize generated list-of-struct capability schemas exactly, while rejecting capabilities for which the SDK has no evaluator
• expose filters_exactly_applied as an explicit opt-in independent of auto-apply
• add focused generated-schema, semantic-profile, and Arrow wire-shape tests

Source-of-truth check

VGI_PYTHON=~/Development/vgi-python scripts/regenerate_protocol.sh produces no diff: the checked-in generated headers already match the current vgi-python 2.0.0 source. This PR closes the handwritten metadata/serializer gap that had caused those generated fields to be silently defaulted empty.

Validation

• cmake --build build -j 8
• ctest --test-dir build --output-on-failure (9/9)
• scripts/format.sh --check
• git diff --check

Dependency

Draft until the Filter-v2 runtime evaluator PR lands. Merging this advertisement first would let a producer send required v2 predicates to the legacy parser, so runtime must merge first (or this commit must be rebased atop it and merged together). No runtime-filter algorithms, extension functions, or session-context provider is advertised.

[rustyconover]

Superseded by validated PR #4, which includes this capability metadata together with the required Filter-v2 evaluator.