Version 4.0.0

Major release aligning the CLI with the polyswarm-api 4.0 SDK (the httpx rewrite).
The command surface and flags are unchanged; the major bump tracks the new 4.0 SDK
dependency. Adds endpoint shortcuts, Known Good Binaries support, and metadata
field-property commands.

New Features

• Environment endpoint shortcuts — --stage, --local, --prod-eu, --stage-eu
  as convenience aliases for --api-uri. With no flag the endpoint defaults to production;
  precedence is explicit flag → POLYSWARM_API_URI env var → production. The shortcuts
  are mutually exclusive with each other and with an explicit --api-uri. (#251)
• polyswarm kgb (Known Good Binaries) command group — create / get / delete
  on a sha256-keyed known-good record. (#248)
• Known-good binary output — the text formatter renders a known-good artifact as a
  known-good binary (with its flagging source) instead of the misleading
  "no engines responded — rescan now". (#250)
• polyswarm search field-property commands — write / get / delete / list
  for metadata field-property entries. Requires an admin API key. (#244)

polyswarm-api 4.0 migration (#245)

Adapts the CLI to the SDK's httpx rewrite with no change to the command surface:

• submit_url routed through the client's _single helper.
• report create downloads via the public report_download().
• Lazy search / ioc generators consumed correctly (incl. per-item no-results
  aggregation for multi-hash search).
• Transport errors matched across httpx exception classes so connection/timeout
  failures still map to exit code 1.

Dependencies & Version

• Bumped version 3.20.0 → 4.0.0.
• polyswarm_api requirement updated from >=3.21.0 to >=4.0.0,<5.0.0 (sync-only).