feat: Add bam::Record::set_cigar

[ctsa]

This is largely modeled off of the existing bam::Record::set_qname method (including its unit test).

The motivation is similar: it's convenient to be able to update just the cigar string of an existing alignment in some cases, without having to re-run much of the bam record data through the set() method.

[coveralls]

Pull Request Test Coverage Report for Build 15793975163

Details

• 23 of 23 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 83.724%

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Totals
Change from base Build 15455217694:	0.1%
Covered Lines:	2747
Relevant Lines:	3281

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💛 - Coveralls