allow for multiple trailing and/or leading whitespace in header

[cjyetman]

No description provided.

[github-actions]

Coverage Report

file	head	main	diff
Overall	58%	58%	0%
R/canonize_path.R	91%	91%	0%
R/determine_headers.R	72%	72%	0%
R/get_csv_specs.R	0%	0%	0%
R/guess_delimiter.R	100%	100%	0%
R/guess_file_encoding.R	89%	89%	0%
R/guess_numerical_mark.R	94%	94%	0%
R/has_binary_null.R	100%	100%	0%
R/has_consistent_fields_per_line.R	100%	100%	0%
R/has_newline_at_end.R	96%	96%	0%
R/is_file_accessible.R	100%	100%	0%
R/is_readable_file.R	100%	100%	0%
R/is_text_file.R	100%	100%	0%
R/is_valid_currency_code.R	100%	100%	0%
R/is_valid_cusip.R	100%	100%	0%
R/is_valid_isin.R	100%	100%	0%
R/read_portfolio_csv.R	86%	86%	0%
R/simplify_if_one_col_df.R	100%	100%	0%

[AlexAxthelm]

@cjyetman I've added a few more tests for more complicated whitespace padding (don't laugh, I've seen these in the wild at other jobs)

[cjyetman]

Checking for tabs seems reasonable to me. Pretty sure the regex should cover any whitespace including tab.