chore: downgrade rust version to nightly-2023-09-18

[StackOverflowExcept1on]

it should fix fuzzer & CI

disadvantages: needless_pass_by_ref_mut warnings (#3452)

[codecov]

Codecov Report

Attention: 352 lines in your changes are missing coverage. Please review.

Comparison is base (bd292dc) 70.72% compared to head (1f8a024) 69.63%.
Report is 28 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3451      +/-   ##
==========================================
- Coverage   70.72%   69.63%   -1.10%     
==========================================
  Files         223      211      -12     
  Lines       24439    29101    +4662     
==========================================
+ Hits        17285    20264    +2979     
- Misses       7154     8837    +1683     

Files	Coverage Δ
common/src/paused_program_storage.rs	91.13% <100.00%> (+0.94%)	⬆️
core-backend/src/env.rs	98.67% <100.00%> (+3.27%)	⬆️
core-backend/src/error.rs	89.47% <ø> (ø)
core-backend/src/runtime.rs	96.80% <100.00%> (-0.06%)	⬇️
core-processor/src/common.rs	85.18% <ø> (ø)
core-processor/src/configs.rs	100.00% <ø> (ø)
core-processor/src/context.rs	89.09% <100.00%> (+0.20%)	⬆️
core-processor/src/executor.rs	93.91% <100.00%> (-0.20%)	⬇️
core-processor/src/processing.rs	99.70% <100.00%> (+<0.01%)	⬆️
core/src/costs.rs	92.59% <100.00%> (+12.21%)	⬆️
... and 70 more

... and 39 files with indirect coverage changes

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