chore: improve let block scoping

[lifeart]

adding part from #25

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[github-actions]

Code Coverage Report

Coverage after merging improve-let-block-scoping into master

74.82%

Coverage Report

File	Lines (%)	Funcs (%)	Uncovered Lines
.../pages/page-one
Smile.ts	71.43		6, 7, 8, 9, ...
.../pages/page-two
Clock.ts	94.29	83.33	18, 27
tests
utils.ts	95.65		31, 75, 76, 77, ...
utils
benchmark.ts	69.44		19, 20, 21, 22, ...
compat.ts	96.23		28, 29, 30, 38, ...
component.ts	96.70		79, 8, 9, 97, ...
dom-api.ts	95.65		12, 21, 22, 23, ...
dom.ts	98.05	92.11	707, 710, 722, 742, ...
ember-inspector.ts	14.70	0	96, 97, 98, 99, ...
if.ts	59.83	66.67	96, 97, 98, 99, ...
list.ts	93.38	80	66, 70, 71, 72, ...
reactive.ts	90.59		66, 67, 85, 86, ...
rehydration-dom-api.ts	50		96, 97, 98, 99, ...
rehydration.ts			135, 144
runtime.ts	95.74		11, 12, 13
shared.ts	76.70		95, 96, 97, 98, ...
vm.ts			24, 4
utils/helpers
hash.ts	81.82	66.67	14, 15, 16, 17, ...
if.ts	66.67		2, 3, 4
utils/inspector
index.ts	33.33	0	96, 97, 98, 99, ...