perf: Extend the JSON-LD fast path to config documents

The initial fast path only covered generator-produced component
documents; hand-written config documents always fell back to the
generic streaming pipeline, which re-resolves type-scoped contexts for
every typed node. Profiling a Community Solid Server cold start showed
those per-node scoped-context activations (1,405 distinct resolutions,
none repeating within a boot) as the dominant remaining parse cost.

This extends the guarded subset with the two features config documents
use:

- Root-level @graph, including the named-graph form (a root node
  carrying properties such as `import` alongside @graph names the graph
  after itself; list cells always land in the default graph, exactly
  mirroring the generic parser's placement).
- Single, non-propagating type-scoped context activation: when a node's
  @type names a term with a scoped context, that scoped context is
  resolved ONCE per (context, term) with the real jsonld-context-parser
  (same options as the generic parser's ParsingContext.parseContext),
  analyzed, cached on the root entry, and applied to that node only,
  with nested nodes reverting to the root context (JSON-LD 1.1
  non-propagation semantics). Multiple scoped types, propagating or
  unresolvable scoped contexts, and scoped terms used as keys still
  fall back.

Also fixes double list wrapping for explicit @list objects under
@container: @list definitions (previously such documents fell back
before reaching the converter, so the case was latent).

Correctness: on the full Community Solid Server 7.1.9 boot corpus (828
component documents + 220 config documents), fast-path output is
rdf-isomorphic to the generic pipeline for all 1048 files on BOTH the
current dependency stack and the componentsjs 5.5.1 stack CSS actually
boots with; 1047/1048 take the fast path (the one holdout uses a
base-relative @type, which the fast path deliberately leaves to the
generic parser). 30 new unit tests cover the @graph and scoped
activation matrices; the suite retains 100% coverage.

Performance (pss-solid-test, 2-core shared box, alternating arms,
fresh data root per boot; backport of this branch onto the installed
componentsjs 5.5.1): CSS cold start drops from a 16.0-17.9 s stock
median of 16.9 s to 6.2-6.5 s (median 6.3 s) - 2.67x, with 977/978
boot documents fast-pathed. Combined with the earlier module-state
work this brings CSS cold boot to the 4-6 s range targeted by the
boot-latency roadmap.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: jeswr