Remove unused WriterTo interface constraint from rarReader type

[dpgarrick]

Issue

The rardecode v2.2.0 library removed the WriterTo method from its Reader and ReadCloser types, causing
compilation failures:

go test ./...
# github.com/mholt/archives [github.com/mholt/archives.test]
./rar.go:105:9: cannot use or (variable of type *rardecode.ReadCloser) as rarReader value in assignment: *rardecode.ReadCloser does not implement rarReader (missing method WriteTo)
./rar.go:109:13: cannot use rardecode.NewReader(sourceArchive, options...) (value of type *rardecode.Reader) as rarReader value in assignment: *rardecode.Reader does not implement rarReader (missing method WriteTo)
FAIL	github.com/mholt/archives [build failed]
FAIL

Solution

Removed io.WriterTo from the rarReader interface definition since it was never actually used in the archives codebase.
The interface now only requires Next() and io.Reader, which are the methods actually utilized by the RAR
extraction implementation.

[Copilot]

Pull Request Overview

This PR fixes a compilation error by removing the unused io.WriterTo interface constraint from the rarReader type definition to maintain compatibility with the updated rardecode v2.2.0 library.

• Removed the unused io.WriterTo method requirement from the rarReader interface
• Updated the rardecode dependency from v2.1.1 to v2.2.0

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
rar.go	Removed io.WriterTo from rarReader interface to fix compilation error
go.mod	Updated rardecode dependency to v2.2.0

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[dpgarrick]

Apologies in advance for the copilot auto review. Not sure why I don't have the option to disable that for external repos!

[mholt]

Are we sure about this? My understanding is many of underlying io functions use WriterTo if it's implemented. So the embedded interface is to help ensure those efficiency paths will be utilized. (I know this is the case at least in HTTP/network contexts.)

[dpgarrick]

The rardecode package doesn't implement WriterTo is the issue

It only decodes rar format, it does not write it

[mholt]

Oh -- duh, you are right. 🤦‍♂️

Not sure how I totally forgot that our RAR is read-only.