Complete jq semantics and make evaluation allocation-aware

[jcelerier]

Problem

The evaluator accepted only part of jq's expression grammar, diverged on several streaming/numeric/error cases, and deep-copied pass-through values at every coroutine boundary. std::function targets and coroutine frames also used the heap without an explicit evaluation lifetime.

Language and semantic changes

• direct recursive-descent compilation with local action trees
• if / elif / else, try / catch, select, and, or, and //
• semicolon-separated filter arguments and the any, all, first, last, isempty, nth, limit, skip, and range arities
• object-value pipelines, computed/streamed slices, nested interpolation, and jq comments
• corrected output order, optional-error scope, lazy early termination, array to_entries, and object map
• exact signed-64-bit comparison/negation, jq NaN equality/ordering, modulo boundaries, and UTF-8 split/slice behavior
• preserve output emitted before a later error, including lazy object construction

Lazy ownership and allocation

• coroutine yields distinguish borrowed and owned values; forwarding no longer materializes pass-through arrays/maps/strings
• prevent accidental promise aggregate initialization from copying coroutine inputs
• caller-backed evaluation_context routes coroutine frames and allocator-aware values through bounded storage
• strict contexts throw on exhaustion; explicit upstream resources retain unbounded compatibility
• take() retains within the selected context; persist() detaches escaping values to heap storage
• exception payloads persist independently of evaluation storage
• compiled actions use stable pointer-owned smallfun nodes instead of recursive std::function targets
• stable index sorting avoids std::stable_sort's hidden allocator

Verification

• standalone build and CTest: 3/3 targets pass
• 356 generated conformance cases pinned to official jq 1.8.2
• ownership tests cover large borrowed inputs, arena reuse, nested evaluation, escaped results/errors, strict exhaustion, and frame deallocation
• allocation smoke: 0 global heap allocations inside a bounded context for identity, length, selection/projection, map, sort, unique, sort_by, group_by, and long literals
• actual score boundary smoke passes proper-map selection, callback-retained output lifetime, and callback-triggered program replacement

The allocator-aware OSSIA conversion support used by the score addon is proposed separately in celtera/avendish#202.