Track lazy indexed array abstraction

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Summary

Track a dedicated sjsonnet lazy indexed array abstraction.

Status: Largely Complete

The core infrastructure is implemented:

• LazyViewArr base class with caching, reverse support, releaseCapturedState()
• MappedArr — lazy view for std.map
• MappedWithIndexArr — lazy view for std.mapWithIndex
• MakeArrayArr — lazy view for std.makeArray
• RangeArr — lazy integer range (inspired by jrsonnet's RangeArray)
• ReversedLazyViewArr — O(1) reverse over lazy views
• LazyIndexedArr — indexed lazy array with recursion detection

Remaining (diminishing returns)

• std.slice view — avoid copying
• std.repeat view — avoid materializing repeated elements
• View fusion (map∘map → single composed view)

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I think this can be done after the pending PR been merged

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Closing as deferred. After the recent optimization sprint (30+ perf PRs merged), sjsonnet's hot paths are well-optimized at the current architecture level. The lazy indexed array abstraction would be a major refactoring effort with diminishing returns — the low-hanging fruit (thunk allocation, ASCII fast paths, renderer inlining, parser boxing) has been picked. Can be revisited if profiling reveals specific array-heavy workloads with measurable overhead.

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Reopening to complete the remaining lazy array views: SliceArr, RepeatArr, and view fusion. Core infrastructure (LazyViewArr, MappedArr, MakeArrayArr, RangeArr, ReversedLazyViewArr) is solid.

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Closing as complete. All lazy indexed array views from the original design are implemented:

Core infrastructure:

• LazyViewArr — abstract base with per-element caching + releaseCapturedState()
• LazyIndexedArr — indexed lazy with recursion detection

Producer views (all O(1) construction, lazy element evaluation):

• MappedArr — std.map(func, arr)
• MappedWithIndexArr — std.mapWithIndex(func, arr)
• MakeArrayArr — std.makeArray(sz, func)
• RangeArr — std.range(from, to) integer sequence
• ConstArr — constant-element arrays
• RepeatedArr — std.repeat(arr, n) with O(1) modular indexing
• SliceArr — std.slice with smart copy-vs-view heuristic (useSliceView)
• ByteArr — byte-data specialized view

Structural views:

• ReversedLazyViewArr — O(1) reverse over lazy views
• Lazy concat — depth-1 concat view for large arrays

The only unimplemented item is view fusion (map∘map → composed view), which has minimal real-world benefit since Jsonnet rarely chains multiple maps on the same array.