fix(fast_check): strip private declare field decorators

[fibibot]

Fixes denoland/deno#33753.\n\nFast-check rewrites TS-private class fields to declaration-style private properties. When the original field has a decorator, the generated output kept that decorator on a declare private field, which TypeScript rejects with TS1206.\n\nThis clears decorators when transforming TS-private class properties into fast-check declaration fields and adds a regression test for the generated source.\n\nAI assisted: yes.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

exe.dev user seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[neonbyte1]

@bartlomieju in which upcoming release can we expect that the issue is resolved? :) 2.8 was just released