fix(toolkit-lib): deployment total time includes stray output

[mrgrain]

Fixes an extra Deployment <number> at the end of the "Total Time" message reporting the total deployment time.

Adds missing test cases for the MessageSpan feature (GenAI supported).

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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 93.54839% with 2 lines in your changes missing coverage. Please review.

Project coverage is 85.38%. Comparing base (cb8a7e0) to head (835338a).

Files with missing lines	Patch %	Lines
...cdk/tmp-toolkit-helpers/src/api/io/private/span.ts	93.54%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #238      +/-   ##
==========================================
+ Coverage   85.09%   85.38%   +0.28%     
==========================================
  Files         206      212       +6     
  Lines       35215    36068     +853     
  Branches     4535     4565      +30     
==========================================
+ Hits        29966    30795     +829     
- Misses       5099     5126      +27     
+ Partials      150      147       -3     

Flag	Coverage Δ
suite.unit	85.38% <93.54%> (+0.28%)	⬆️

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[kaizencc]

small comment

[kaizencc]

meta question for my benefit: what did you ask AI for, and how many iterations did it take for it to get it right?

[mrgrain]

To write the tests. Took about 4 iterations and some manual fixing in between.