feat: providers result limits for JSON and NDJSON

[lidel]

Someguy supports JSON (buffered) and NDJSON (streaming) response types.

Problem

JSON delegated routing responses under-delivered: iiuc boxo's DefaultRecordsLimit of 20 acted as a pre-filter, and cacheFallbackIter silently dropped records without addresses.

Anecdotally (cc @aschmahmann), production at delegated-ipfs.dev returned ~4 providers on JSON (when opened in browser) vs ~17 on NDJSON for the same CID (/ipns/ipfs.tech).

As a side problem, NDJSON stream had no cap, which is a bad default.

Fix (This PR)

• raise the JSON cap to 100 and add a streaming cap of 1000, matching HTTP Routing v1 section 4.1.5; expose both as --records-limit and --streaming-records-limit with SOMEGUY_* env vars; reject negative input, 0 disables the cap
• over-fetch from the underlying router by 3x (cap 3000) so that, after cacheFallbackIter drops addr-less records, the surfaced count is close to the caller's limit; cap the final stream via a new limitedIter wrapper
  • not a fan of over-fetching, but these are mostly theoretical caps, most of CIDs will never hit 1k any time soon, and if we hit that ever, should be more than enough for retrieval (and a good problem to have)