[47] Fix quest complete item reward trailer

[alseif0x]

Refs #57

QA pending: do not merge until packet capture validation, CI, and Codex reviewer verdict are complete. This is a partial #57 slice and must not close the issue.

Summary:

• Implements the QUESTPKT.3 slice by serializing the trailing ItemReward ItemInstance in SMSG_QUEST_GIVER_QUEST_COMPLETE.
• Adds byte-level tests for the empty ItemInstance trailer and flag branches.
• Documents remaining QUESTPKT.1, QUESTPKT.2, and QUESTREWARD.1 gaps.

Validation reported locally:

• PROTOC=/home/cdmonio/.local/protoc/bin/protoc cargo test -p wow-packet --lib
• PROTOC=/home/cdmonio/.local/protoc/bin/protoc cargo test -p wow-packet quest_giver_quest_complete --lib
• cargo fmt --all -- --check
• git diff --check

Manual QA pending: capture quest-complete packet against C++.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 60f6b9e59d

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[alseif0x]

@codex review

[alseif0x]

QA validation checklist:

• Complete a quest with no item reward and confirm the completion/reward window behaves normally.
• Complete a quest with a fixed item reward and confirm the item appears correctly and accepting the reward completes the quest.
• Complete a quest with selectable item rewards if available; selecting one should work without disconnect, packet parse errors, or shifted/missing reward data.
• Watch for client crashes, server packet errors, or reward UI corruption around quest-complete flows.

Note: this PR still needs the Codex reviewer verdict green on the current head before it is merge-ready.

[alseif0x]

@codex review

The previous Codex reviewer verdict run timed out waiting for a clean review on current HEAD 39def6dcb4; it did not report new actionable feedback. Please review the current head again.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Delightful!

Reviewed commit: 39def6dcb4

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".