AWS: Optimize Iceberg-to-Glue schema type conversion

[wombatu-kun]

Follow-up to #16735, which replaced the per-node String.format recursion in HiveSchemaUtil.convertToTypeString with a single StringBuilder. This applies the same optimization to the analogous Glue path, IcebergToGlueConverter.toTypeString, which runs on every Glue create/update commit (via setTableInputInformation -> toColumns, which also re-converts every schema in the table's schema history).

The previous code allocated at every level of the type tree: a String.format per node (format-template parse, varargs array, autoboxing of decimal precision/scale, locale lookup), a Stream/Collector/StringJoiner per struct, and it re-copied each child type string into its parent (superlinear for deeply nested types). The rewrite threads a single StringBuilder through the recursion and appends directly, so each character is written once. The produced type strings are byte-identical, and toTypeString's signature and all call sites are unchanged.

This is a performance and readability change only, with no behavior change: Glue's default case already rendered VARIANT and other types without error, so there is no correctness component here.

Benchmark

A JMH benchmark over three schema shapes (avg time and gc.alloc.rate.norm, JDK 21, 1 fork, 5+5 iterations, -prof gc). The benchmark is not included in this PR.

Schema shape	avg time us/op (before -> after)	alloc B/op (before -> after)
WIDE_FLAT (200 primitive cols, control)	52.1 -> 48.3 (-7%)	141,384 -> 138,984 (-2%)
DEEPLY_NESTED (~10-deep struct/list/map)	6.1 -> 1.1 (-82%)	21,008 -> 2,680 (-87%)
WIDE_NESTED_MIX (100 mixed cols)	68.5 -> 28.4 (-59%)	127,256 -> 76,968 (-40%)

WIDE_FLAT is a control dominated by per-column Column/ImmutableMap building that this change does not touch, so it stays roughly flat; the win grows with nesting depth and the number of nested columns. Allocation figures are deterministic; the WIDE_NESTED_MIX baseline time had high run-to-run variance, so its allocation reduction is the reliable measure there. Existing TestIcebergToGlueConverter continues to pass, pinning the byte-identical output.

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AI Disclosure

• Model: Claude Opus 4.8
• Platform/Tool: Claude Code
• Human Oversight: fully reviewed
• Prompt Summary: Replace the per-node String.format recursion in IcebergToGlueConverter.toTypeString with a single StringBuilder.

[github-actions]

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[wombatu-kun]

not stlae