ENH: Better error message when input alignment has sequences of unequal length

[corneliusroemer]

I got this error from refine that I struggled to debug:

ERROR: SequenceData: loading alignment failed... builds/masked.fasta

ERROR from TreeTime: This error is most likely due to a problem with your input data.
Please check your input data and try again. If you continue to have problems, please open a new issue including
the original command and the error above:  <https://github.com/nextstrain/augur/issues/new/choose> 

I didn't know why the alignment couldn't be loaded.

Turns out, my sequences weren't aligned, they had different lengths.

Would be good to report a bit more granular detail from what goes wrong in the alignment loading.

[corneliusroemer]

Error should be handled here:

treetime/treetime/sequence_data.py

Lines 154 to 159 in 52e7cd1

	else:
	for fmt in ['fasta', 'phylip-relaxed', 'nexus']:
	try:
	in_aln=AlignIO.read(in_aln, fmt)
	except:
	continue

See https://bedfordlab.slack.com/archives/C01LCTT7JNN/p1694021182135669?thread_ts=1694018285.407369&cid=C01LCTT7JNN