fix: split long PR comments into multiple parts to avoid GitHub API limit

[raman1236]

Description

Fixes #1645 — GitHub enforces a 65535 character limit on issue/PR comment bodies. When terraform plan output is large (common with infrastructure-heavy repos), the entire comment post fails with exit code 5, leaving users with no plan output at all.

Problem

Users with large infrastructure see this error:

ERROR 422 Validation Failed [{Resource:IssueComment Field:body Code:custom Message:body is too long (maximum is 65536 characters)}]

The job crashes and no plan output is posted to the PR.

Solution

Modified GithubService.PublishComment() to automatically split comments exceeding 65000 characters into multiple parts:

1. Each part is prefixed with **Part X/Y** header for clarity
2. Splitting tries to break at newline boundaries to preserve markdown readability
3. If no good newline is found in the second half, falls back to a hard split at the limit
4. Short comments (under the limit) are posted as-is with zero overhead

Changes

• libs/ci/github/github.go: Added splitComment() helper and updated PublishComment() to split long comments
• libs/ci/github/github_test.go: Added 3 unit tests covering short, long, and exact-limit cases

Testing

=== RUN   TestSplitComment_ShortComment
--- PASS
=== RUN   TestSplitComment_LongComment
--- PASS  (verifies no content loss, all parts within limit)
=== RUN   TestSplitComment_ExactLimit
--- PASS

[tanguyantoine]

this would be awesome, is this implemented?