deepObject: bracket-indexed arrays and nested objects

[tanmaykm]

Fixes #110.

Summary

deepObject query parameters with array schemas or nested object/array values worked in 0.2 (added in #78) but not in 1.0.0: strict rejected the schema, permissive planned it and then failed every request, and the client encoder threw on nested values. This restores end-to-end support using the bracket convention that qs, Rack and PHP produce, as a documented extension accepted at strict.

filters[0][field]=severity&filters[0][values][0]=error&filters[0][values][1]=warning
sorts[0]=-created_at&sorts[1]=%2Bname

Changes

• Planning (src/planning.jl): array schemas under deepObject plan at strict without diagnostics. Only scalar schemas still emit invalid_deep_object_schema (error at strict, warning at permissive).
• Client encoder (src/runtime.jl): nested dicts and vectors flatten recursively into indexed bracket paths. Arrays now encode as name[0]=… rather than name[]=…, matching the 0.2 encoder and the qs default. The multipart deepObject encoder shares the helper.
• Server decoder (src/servergen.jl + src/runtime.jl): full bracket paths (including percent-encoded brackets and name[] appends) build a tree, and a schema-guided pass rebuilds it in the declared shape before validation. Integer keys become array indices only where the schema expects an array, so an additionalProperties object keeps "0" as a string key. Leaves stay text where the schema says string, so sorts[0]=2024 is no longer read as an integer. $ref, allOf, oneOf and anyOf are followed.
• Schema engine: adds a generic non-throwing trysubschema accessor.
• Docs: new "deepObject bracket paths" section in the servers manual, linked from the clients manual; the boundary page now lists only scalar deepObject as a permissive case.
• Version: 1.1.0, since strict mode accepts new input.

Decisions worth a look

1. Arrays of scalars now encode indexed (expand[0]=a&expand[1]=b) instead of expand[]=a&expand[]=b. The server accepts both forms; this is a visible client wire change from 1.0.0.
2. Arrays are accepted at strict with no diagnostic. An informational note would be a one-line change in the planner if preferred.

Verification

• The reproduction from deepObject: bracket-indexed arrays and nested objects (supported in 0.2 via #78) no longer work in 1.0 #110 returns 200 with typed models in strict mode for both spec variants, and the client emits filters[0][field]=… pairs.
• Full suite on Julia 1.12.7 passes, including a new server-level testset covering the qs wire format, [] appends, encoded brackets, sparse indices, the array-vs-object-key decision, string leaves, and 400s for invalid shapes. Julia 1.10 was not available locally.
• OPENAPI_CORPUS_TESTS=small passes. Docs build passes and the new cross-reference resolves.
• The checked-in JuliaC --trim=safe workload still passes. Note that the request/response runtime paths (query encoding, JSON decode, schema validation) were not trim-safe before this change and are not made so here; a widened trim workload fails the same way before and after.