[#1178] Add loom test for spsc index queue

[mox692]

Notes for Reviewer

Ref: #1178

This PR adds loom test for spsc_index_queue. The UnsafeCell and other atomic types that are used in the index queue will use loom types during the loom test (#1194).

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• Add sensible notes for the reviewer
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PR Reviewer Reminders

• Commits are properly organized and messages are according to the guideline
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[orecham]

@mox692

Had to make some tweaks to resolve some conflicts in: #1204
If I broke something by mistake feel free to ping me.