feat: add TSA and certificate support to wasm signer

[thillmann]

When trying to use the Builder to embed a signed manifest in a media file, we encountered a few gaps:

• direct_cose_handling was always set to true
• There was no way to pass certificates down to the signing process
• There were a few more options missing on Signer

Using the Node.js implementation as guidance, I made those changes and confirmed it was working in our sign and embedding flow.