fix: alloc(0) call is UB

[EmilyMatt]

When calling alloc(), the layout must be non-zero, otherwise we fall into undefined behaviour.
This is documented in the function's docs:
https://doc.rust-lang.org/beta/src/core/alloc/global.rs.html#152

We can just make a dangling pointer for those cases, and not deallocate it

Found by running miri on tests::test_send_sync

[Licenser]

Thank you! good catch :)

[EmilyMatt]

@Licenser Does this have anything actionable for me? or is just pending due to time limitations?

[EmilyMatt]

I'm fixing CI here(some clippy warnings and wastime installation)
Will rebase the other PR (#445 ) after this is merged

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.16%. Comparing base (c18bb92) to head (3084cb7).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #442      +/-   ##
==========================================
- Coverage   72.33%   72.16%   -0.17%     
==========================================
  Files          51       49       -2     
  Lines       11435    11318     -117     
==========================================
- Hits         8271     8168     -103     
+ Misses       3164     3150      -14     

Flag	Coverage Δ
unittests	72.16% <100.00%> (-0.17%)	⬇️

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[EmilyMatt]

@Licenser Last two checks can't be green until merged to main (I think they will only be green in the next PRs)