feat: Replace serde_qs to serde_html_form

[sugyan]

fixes #160

serde_qs was introduced in #25, and it did indeed correctly serialize parameters, even those that contained arrays.
However, the serialized result is a format like uris[0]=at%3A%2F%2Fdid%3A...&uris[1]=at%3A%2F%2Fdid%3A..., and this behavior does not seem to be changeable.
Not that this format is wrong, but it seems to cause problems when used in requests to servers that work with express, such as bluesky's appview.

Specifically, in the qs library used by express, if we specify an index larger than 20 by [] notation, it is treated as an object key, and the query in the request is not correctly passed as an array.
https://www.npmjs.com/package/qs#parsing-arrays

It would seem that this behavior could be avoided if it could be serialized with a format that does not include an index, such as uris=at%3A%2F%2Fdid%3A...&uris=at%3A%2F%2Fdid%3A....
There is a crate called serde_html_form that does exactly that and is used in axum and others.
Replacing serde_qs with this library would solve the problem.