chore(ci): Adds nightly and release build workflows

- Introduces workflows for nightly and release builds,
  automating package publishing to Gitea.
- Includes scripts for setting Poetry version, cleaning up
  old dev versions, and uploading assets to releases.
- Adds a merge template for pull requests.

.gitea/default_merge_message/MERGE_TEMPLATE.md

@@ -0,0 +1,5 @@
+chore(pr): ${PullRequestTitle} ${PullRequestReference}
+
+${PullRequestDescription}
+
+Merged from ${HeadBranch} into ${BaseBranch}