Add Chocolatey ecosystem support

[andrew]

Adds support for indexing Windows packages from the Chocolatey community repository.

Uses the NuGet v2 OData feed at community.chocolatey.org/api/v2:

• FindPackagesById()?id='name' for per-package metadata, following <link rel="next"> to collect all versions
• Packages()?$filter=IsLatestVersion&$select=Id with skiptoken pagination for the full name list (server hard-caps pages at 40 entries, so ~250 requests for ~10k packages on a full sync)
• feeds.feedburner.com/chocolatey for recently updated (the OData $orderby parameter is rejected by this server)

Maps ProjectSourceUrl → repository_url with ProjectUrl fallback, Tags → keywords, DownloadCount → downloads (max across version entries since the latest entry sometimes reports 0), PackageHash → integrity. Dependencies are parsed from the OData name:range:framework|... string format. purl type is chocolatey, install command is choco install NAME --version=X.

The OData $count endpoint caps at 10000 so the true package count may be higher; skiptoken pagination walks past that regardless.

To enable in production:

Registry.find_or_create_by(name: 'community.chocolatey.org', url: 'https://community.chocolatey.org', ecosystem: 'chocolatey', github: 'chocolatey', default: true).sync_all_packages_async

Closes #1617