feature (minor): Per-parameter URL encoding opt-out (Retrofit encoded=true equivalent) #2169

Summary

Refit encodes URL [Query] and path segment values automatically, and the only controls are method-level ([QueryUriFormat]) or coarse (TreatAsString). There's no per-parameter way to say "this value is already encoded, pass it through verbatim." This is the feature side of bug #2002 (URL segments getting encoded with no toggle).

Prior art: Retrofit encoded

Retrofit puts an encoded flag on individual parameter annotations — @Query(value, encoded=true), @Path(value, encoded=true), @Field(..., encoded=true), @QueryMap(encoded=true). When set, Retrofit skips URL-encoding for that parameter, letting callers pass pre-encoded values.

Proposal

Add a per-parameter encoding opt-out, e.g. an Encode = false property on [Query] (and a path equivalent), so a single value can bypass automatic encoding while the rest of the request encodes normally. Resolves #2002.

Considerations

• Interaction with UrlResolutionMode (RefitLegacy vs Rfc3986) and QueryUriFormatAttribute — define precedence (per-param should win).
• Path-segment opt-out is the case [Bug]: URL Segments getting encoded, with seemingly no way to toggle this #2002 specifically hits; cover both query and path.
• Reflection + source-generator paths.
• Document the footgun: caller becomes responsible for producing valid encoded output.

Acceptance criteria

• A per-parameter switch that passes a query/path value through without encoding.
• Closes [Bug]: URL Segments getting encoded, with seemingly no way to toggle this #2002 (path segment case verified).
• TUnit tests for query and path; README/docs entry.

Pointers

• Query/path building: src/Refit/RequestBuilderImplementation.RequestBuilding.cs, RequestBuilderImplementation.QueryAndHeaders.cs.
• Existing attribute: src/Refit/QueryAttribute.cs (TreatAsString, Format), src/Refit/QueryUriFormatAttribute.cs.
• Related: [Bug]: URL Segments getting encoded, with seemingly no way to toggle this #2002, Support non-string round-tripping parameters #2046.
• Retrofit reference: ~/square/retrofit/retrofit/src/main/java/retrofit2/http/{Query,Path,Field}.java.