feat(toolkit-lib): structured log monitoring events

[mrgrain]

Moves more of the APIs to use modern IO infrastructure.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 83.72093% with 14 lines in your changes missing coverage. Please review.

Project coverage is 85.06%. Comparing base (84d0b54) to head (9e4745b).

Files with missing lines	Patch %	Lines
packages/aws-cdk/lib/api/logs/logs-monitor.ts	88.46%	9 Missing ⚠️
packages/aws-cdk/lib/cli/cdk-toolkit.ts	33.33%	4 Missing ⚠️
...kages/aws-cdk/lib/api/logs/find-cloudwatch-logs.ts	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #218      +/-   ##
==========================================
+ Coverage   85.00%   85.06%   +0.05%     
==========================================
  Files         208      208              
  Lines       35563    35591      +28     
  Branches     4627     4623       -4     
==========================================
+ Hits        30230    30275      +45     
+ Misses       5175     5165      -10     
+ Partials      158      151       -7     

Flag	Coverage Δ
suite.unit	85.06% <83.72%> (+0.05%)	⬆️

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