Add functionality for reading and writing alignments from/to A3M format

[padix-key]

Resolves #724.

[codspeed-hq]

CodSpeed Performance Report

Merging #848 will not alter performance

_{Comparing padix-key:a3m (557e182) with main (cee6735)}

Summary

✅ 60 untouched
🆕 3 new

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
🆕	benchmark_get_sequences[fasta_path0-NucleotideSequence]	N/A	184.1 ms	N/A
🆕	benchmark_get_sequences[fasta_path1-ProteinSequence]	N/A	8.9 ms	N/A
🆕	benchmark_get_a3m_alignments	N/A	579.4 ms	N/A