Introduce support for missing GitHub event types

## Problem
Currently, the action only serializes a fixed set of GitHub event types (IssueCommentEvent, IssuesEvent, PullRequestEvent, ReleaseEvent). Other event types, such as `PullRequestReviewEvent`, `PushEvent`, `ForkEvent`, `WatchEvent`, and more, are ignored and do not show up in the activity readme.

## Proposal
- Add serialization functions for meaningful additional event types (e.g., PullRequestReviewEvent, PushEvent, ForkEvent, etc.).
https://docs.github.com/en/rest/using-the-rest-api/github-event-types?apiVersion=2022-11-28
- Ignore noisy or non-informative events like WatchEvents

Start by reading the existing serialization for IssueCommentEvent, IssuesEvent, PullRequestEvent, and ReleaseEvent, then compare the GitHub event types documentation linked in the issue. Add meaningful serializers for selected events such as PullRequestReviewEvent, PushEvent, and ForkEvent while excluding noisy events like WatchEvent, and verify that they appear correctly in the activity README.

Written by the indexing model from the issue text.