[core, lua, test] Scripted respawns fixes

[sruon]

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• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• I have read and understood the Contributing Guide and the Code of Conduct.
• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Mobs with respawn time set to 0 in SQL (SPAWNTYPE_SCRIPTED) but setRespawnTime in initialize are being set to never spawn.

• Adds the condition to register them if the onMobInitialize call specified a new respawn timer
• Modify setRespawnTimer to treat 0 as a disable
• Modify getRespawnTimer to return the actual remaining time
• Tweaks the way Noble Mold and Ereshkigal re-registers the PH
• Adds tests for Simurgh and King Arthro

Steps to test these changes