feat: Add to_vcf_string method for bcf::Record

[ctsa]

We have a use case (PacificBiosciences/HiFiCNV#31) where some element of an input vcf/bcf record is surprising, and the program needs to error out. To make the error message as informative as possible for this case we'd like to print the problematic vcf record in the error message.

I'm proposing to add a new to_vcf_string method to bcf::Record as a solution to this issue.

[coveralls]

Pull Request Test Coverage Report for Build 11799729563

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 10 of 11 (90.91%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 79.757%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/bcf/record.rs	10	11	90.91%

Totals
Change from base Build 11799687230:	0.04%
Covered Lines:	2498
Relevant Lines:	3132

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💛 - Coveralls