Split out lib from CLI code

[eheikes]

• Moves shared/SDK code from tts-cli into tts-lib.
• Cleans up and modernizes the code.
• Replaces fs-extra package with native fs routines.

[codecov]

Codecov Report

Attention: Patch coverage is 99.04762% with 3 lines in your changes missing coverage. Please review.

Project coverage is 99.31%. Comparing base (d67c14a) to head (4634a3e).

Files with missing lines	Patch %	Lines
packages/tts-lib/lib/generate-all.js	77.77%	2 Missing ⚠️
packages/tts-lib/lib/provider.js	98.43%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #155      +/-   ##
===========================================
- Coverage   100.00%   99.31%   -0.69%     
===========================================
  Files           13       17       +4     
  Lines          349      436      +87     
===========================================
+ Hits           349      433      +84     
- Misses           0        3       +3     

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	husky@​9.1.7
	proxyquire@​1.8.0 ⏵ 2.1.3			+1
	commander@​14.0.0
	execa@​9.6.0
	@​google-cloud/​text-to-speech@​5.0.1 ⏵ 6.2.0				+2

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