Rename jsonc → jsonx, add JSONL/NDJSON support

[milo-oaklight]

Summary

Rename the jsonc module to jsonx ("extended JSON") and add JSONL/NDJSON parsing support.

Motivation

• Current jsonc module only handles single JSON documents with comments/trailing commas
• JSONL (JSON Lines / NDJSON) is widely used for LLM training data, structured logs, and streaming — but not supported
• Renaming now (while adoption is small) avoids future breakage when adding more JSON variants

Affected repos (from scan)

Direct users: ToolRegistry, matrixd, zerodep/config (vendored _vendor/jsonc.py)
Hand-rolled equivalent: llm-rosetta (_strip_jsonc_comments() in gateway/config.py)
Indirect (via ToolRegistry): toolregistry-hub, toolregistry-server

Scope

1. Rename jsonc/ → jsonx/

• Rename directory and module file
• Update manifest.json entry
• Update internal imports (zerodep config module references jsonc)

2. Add JSONL/NDJSON support

New public API:

from jsonx import loads_lines, load_lines   # JSONL/NDJSON parsing
from jsonx import dumps_lines, dump_lines   # JSONL/NDJSON serialization

• loads_lines(text) → list[Any] — parse multi-line JSONL string
• load_lines(fp) → list[Any] — parse JSONL from file-like object
• dumps_lines(items) → str — serialize list to JSONL string
• dump_lines(items, fp) → write JSONL to file-like object
• Each line goes through the existing JSONC preprocessor (comments + trailing commas stripped), so JSONL-with-comments works out of the box

3. CLI backward compatibility

Add replaced_by mechanism to manifest.json + CLI:

• Old jsonc manifest entry gets "replaced_by": "jsonx"
• zerodep add jsonc → installs jsonx with a note
• zerodep outdated → detects local jsonc.py, shows rename suggestion
• No symlink needed

4. Update tests & benchmarks

• Rename test files: test_jsonc_* → test_jsonx_*
• Correctness tests: add JSONL cases (multi-line, empty lines, comments in JSONL, mixed types)
• Benchmark: add JSONL benchmarks comparing against:
  • jsonlines (most popular JSONL lib)
  • ndjson (API closest to stdlib json style)
• Keep existing JSONC benchmarks against commentjson

5. Downstream migration (separate PRs)

• ToolRegistry — _vendor/jsonc.py → _vendor/jsonx.py
• matrixd — _vendor/jsonc.py → _vendor/jsonx.py
• zerodep/config — internal import update
• llm-rosetta — replace hand-rolled _strip_jsonc_comments() with jsonx

Non-goals

• JSON5 support (future consideration, significantly more work)
• Binary formats (BSON, CBOR, MessagePack — different domain)
• Streaming/iterator API (can add later if needed)

Existing API (preserved, re-exported from jsonx)

• loads(), load() — JSONC single-document parsing
• dumps(), dump() — JSON serialization (stdlib passthrough)
• JSONCDecodeError — error class with line-number remapping