Refactor all plugins to functional options pattern

[Copilot]

All plugin constructors previously used direct struct instantiation with exported types, mixing JSON parsing, validation, and construction logic in a single new* function. This refactors every plugin in plugin/ subdirectories to match the functional options pattern established by plugin/singbox/srs_in.go / srs_out.go.

Changes

Pattern applied uniformly across all plugins

• Struct types made unexported (lowercase)
• New*(action, opts...) constructor accepting variadic lib.InputOption / lib.OutputOption
• With*() option functions per configurable field (with validation via log.Fatalf for required/exclusive options, matching the reference)
• New*FromBytes(action, data) for JSON-based construction, called from init()

Shared-constructor plugins (maxmind, plaintext)

These packages share one struct across multiple registered types (e.g. geoLite2CountryMMDBIn serves maxmindMMDB, dbipCountryMMDB, ipinfoCountryMMDB). Constructors and option functions take iType/iDesc as explicit parameters to carry type identity:

// common_in.go
func NewGeoLite2CountryMMDBIn(iType, iDesc string, action lib.Action, opts ...lib.InputOption) lib.InputConverter

// dbip_country_mmdb_in.go init()
lib.RegisterInputConfigCreator(TypeDBIPCountryMMDBIn, func(action lib.Action, data json.RawMessage) (lib.InputConverter, error) {
    return NewGeoLite2CountryMMDBInFromBytes(TypeDBIPCountryMMDBIn, DescDBIPCountryMMDBIn, action, data)
})

Callers updated

lookup.go and merge.go (which previously used struct literals with exported fields) are updated to use the new constructors.

Files changed

• plugin/mihomo: mrs_in.go, mrs_out.go
• plugin/v2ray: dat_in.go, dat_out.go
• plugin/special: cutter.go, lookup.go, private.go, stdin.go, stdout.go, test.go
• plugin/maxmind: common_in.go, common_out.go, all *_mmdb_{in,out}.go, maxmind_asn_csv_in.go, maxmind_country_csv_in.go
• plugin/plaintext: common_{in,out}.go, text_{in,out}.go, clash_{in,out}.go, surge_{in,out}.go, json_in.go
• Root: lookup.go, merge.go