Use initialization-on-demand holder instead of double-checked locking

[howlger]

Use the initialization-on-demand holder idiom instead of the double-checked locking idiom as the first one is a bit faster and better to read.

See https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom

[github-actions[bot]]

Test Results

1 214 files  +1 214  1 214 suites  +1 214   1h 4m 27s ⏱️ + 1h 4m 27s 4 174 tests +4 174  4 128 ✅ +4 128   46 💤 + 46  0 ❌ ±0  9 541 runs  +9 541  9 420 ✅ +9 420  121 💤 +121  0 ❌ ±0 

Results for commit 5e7323da. ± Comparison against base commit 083f7afd.