Refactor plugins to use validated functional options

[Copilot]

Plugin construction mixed JSON decoding, defaults, and validation across exported implementations. This refactor applies functional options to every converter and validates documented requirements before returning.

• Construction

  • Add New*, With*, and New*FromBytes APIs.
  • Make converter implementations private.
  • Preserve format-specific defaults and JSON behavior.

• Validation

  • Pair name and uri in one option.
  • Make inputDir the mutually exclusive alternative.
  • Validate required fields such as jsonPath, wantedList, search, and V2Ray uri.

• Integration

  • Replace direct struct construction in lookup and merge commands.
  • Ensure directory lookup supplies only inputDir.

input := mihomo.NewMRSIn(
    lib.ActionAdd,
    mihomo.WithNameAndURI("cn", uri),
    mihomo.WithInputWantedList([]string{"cn"}),
)

[Loyalsoldier]

@claude[agent] Review this PR, try to refine it and find potential bugs.

[Loyalsoldier]

@codex[agent] Review this PR, try to refine it and find potential bugs.

[Claude]

@claude[agent] Review this PR, try to refine it and find potential bugs.

Reviewed the whole diff. One real regression found and fixed in f91e24c:

lookup -d <dir> with a single-file format (maxmindMMDB, dbipCountryMMDB, ipinfoCountryMMDB, v2rayGeoIPDat) silently ignored dir. Previously those built a struct literal with an empty URI and failed; now they go through New*In, which applies the plugin's default input path, so it would silently read e.g. ./geolite2/GeoLite2-Country.mmdb instead. Those formats now reject dir explicitly.

Two things I left as-is but worth your call:

1. New*FromBytes still returns error, but all validation failures inside New* go through log.Fatal, so config errors abort the process instead of propagating to lib/config.go. This convention comes from the base branch (refactor-plugin-2), so I did not change it. If you want config-driven errors to stay recoverable, the validation blocks could be split into a validate() error used by New*FromBytes while New* keeps fatal behavior.
2. Option functions use bare type assertions (e.g. special.WithName only works with *stdin, plaintext.WithJSONPath only with *text_in), so misuse panics rather than failing at compile time. That's inherent to lib.InputOption/lib.OutputOption being interface-typed; the type-switch + panic("unsupported input converter") in maxmind/common_in.go and special/cutter.go is at least explicit.

Verified with go build ./..., go vet ./..., go test ./..., plus lookup smoke tests for both -u and -d modes.

[Codex]

@codex[agent] Review this PR, try to refine it and find potential bugs.

Reviewed the PR and fixed a validation regression in b3bf254: JSON config creators now return validation errors instead of exiting via public constructors. Local go test ./..., go build ./, secret scan, and CodeQL validation passed.