feat(index): support array object paths in JSON FTS

[wirybeaver]

Summary:

• Emit legacy, wildcard, and exact indexed path tokens for JSON arrays.
• Normalize JSON query triplets with JSONPath-style roots, wildcards, and indexes.
• Add tokenizer and dataset regressions for array-of-object JSON FTS.

Example:
Given this JSON document:

{
  "addresses": [
    {"country": "us", "street": "main"},
    {"country": "ca", "street": "second"}
  ]
}

The JSON FTS tokenizer now emits path variants that let callers search both array values and exact array positions:

addresses.country,str,us        // legacy path, preserves existing behavior
addresses..country,str,us       // wildcard path for addresses[*].country
addresses[0].country,str,us     // exact indexed path
addresses.$index,number,0       // array element position

This means:

• addresses[*].country,str,us matches rows with any address whose country is us.
• addresses[0].country,str,us matches only rows whose first address has country us.
• Mixed nested paths are normalized too, e.g. addresses[*].types[1] becomes addresses..types[1].

Pinot references:

• JSON flattening behavior and array index keys: JsonUtils.flatten
• Mutable JSON index SPI, including write entrypoint and reader inheritance: MutableJsonIndex
• Immutable JSON index writer SPI: JsonIndexCreator
• Immutable JSON index reader SPI: JsonIndexReader

Test Plan:

• cargo fmt --all --check
• cargo test -p lance-index --features "protoc lance-encoding/protoc lance-file/protoc lance-table/protoc lance-datafusion/protoc" scalar::inverted::tokenizer::document_tokenizer::tests -- --nocapture
• PROTOC=/home/user/lance-json/target/debug/build/protobuf-src-0bbb645409253599/out/bin/protoc-27.2.0 cargo test -p lance --features "protoc lance-encoding/protoc lance-file/protoc lance-index/protoc lance-table/protoc lance-datafusion/protoc" test_json_inverted_ -- --nocapture
• PROTOC=/home/user/lance-json/target/debug/build/protobuf-src-0bbb645409253599/out/bin/protoc-27.2.0 cargo clippy --all --tests --benches -- -D warnings