[-] fix duplicate source names in YAML configs, fixes #630

[amrdb]

Fixes issue #630

(Hi, this is part of my preparation for GSoC 25)

[coveralls]

Pull Request Test Coverage Report for Build 13155279833

Details

• 12 of 12 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 30.206%

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Totals
Change from base Build 13111678393:	0.1%
Covered Lines:	1484
Relevant Lines:	4913

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💛 - Coveralls

[pashagolub]

Thanks for your work! I decided to move duplicated functionality to the special routine Sources.Validadte(). That will give us the opportunity to use the same validation methods for all source readers.

Also I used a map[string]any{} instead of []string for uniqueness check. The idea behind is:

1. map with empty struct holds less space than slice
2. the random access is O(1) instead of O(n)

Otherwise the code looks solid and I especially like that you've added unit testing without further remind. :)