Preserve optional Swagger parameters as option types

[Smaug123]

Fifth fix split out of #540; stacked on #545.

SwaggerParameter.Required was parsed but discarded, so every generated parameter was unconditionally mandatory, even though Swagger 2 defaults non-path parameters to optional. Query parameters without required: true are now option-typed (path parameters stay required per the spec; optional bodies are not modelled), e.g. AdminCronList(page : int option, limit : int option).

To support that, the HTTP client generator now understands option-typed [<Query>] parameters: the query string is computed at runtime as a List.choose/String.concat over per-parameter string option components, and appended (with separator) only when nonempty — so None is omitted from the URL and an all-None query leaves the URL bare. Required-only query strings are byte-identical to before. (The joining lambda is deliberately not id, which Gitea methods shadow with a parameter of that name.)

Tests were written first and observed failing (page=Some%283%29 in the URL): TestOptionalQueryParam.fs covers mixed present/missing/escaped/bare cases through a hand-written interface, and TestGiteaClient.fs gains end-to-end AdminCronList coverage for both None and Some.

Note: #541 rewrites this same query-string block off main to fix list-typed parameters; whichever merges second conflicts there. Reconciliation: unify on string list components, mapping optional scalars via Option.toList.

🤖 Generated with Claude Code

[Smaug123]

At the very least this should probably come with a major version bump

[Smaug123]

Hmm. I really don't like this change and I think it probably shouldn't go in. People are presumably not diligently annotating all their parameters as "required", so this will cause so much noise.