feat: Add fasta::build function + FaidxBuildError

[PB-DB]

Adds rust_htslib::faidx::build, which builds a fasta index without a CLI call/external runtime dependency with a doctest.

Additionally adds FaidxBuildError enum entry to rust_htslib::errors::Error.

[coveralls]

Pull Request Test Coverage Report for Build 8021003689

Details

• -1 of 13 (92.31%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 79.85%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/faidx/mod.rs	12	13	92.31%

Totals
Change from base Build 8010520476:	0.06%
Covered Lines:	2453
Relevant Lines:	3072

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💛 - Coveralls