Promote manifest bounds after schema evolution

[osipovartem]

Summary

• promote existing int lower/upper bounds to long when a manifest is rewritten under an evolved schema
• promote existing float bounds to double through the same metadata-only path
• apply promotion in both existing-manifest rewrite constructors and cover lower/upper bounds with a focused unit test

Why

Iceberg allows int -> long, float -> double, and decimal precision widening without rewriting data files. When an append rewrites existing manifest entries under the current schema, old four-byte int/float bounds must be promoted before the new manifest is serialized. Otherwise readers decode those bytes using the widened schema and fail with could not convert slice to array. Decimal bounds need no byte rewrite because their minimal two's-complement encoding is precision-independent.

This is a manifest-metadata path only; it adds no per-row conversion or query execution overhead.

Validation

• cargo +1.95.0 test -p iceberg-rust-spec promotes_manifest_bounds_to_evolved_schema
• cargo +1.95.0 check -p iceberg-rust
• cargo +1.95.0 clippy -p iceberg-rust-spec -p iceberg-rust --all-targets -- -D warnings
• Rustice integration: append before and after int -> long, float -> double, and decimal precision widening; reload catalog; read both files; exercise predicate pruning