Map a resolution string to its interval in seconds. Returns null for
calendar-variable resolutions ('1M' months) where a fixed second-count
would produce false gaps, and for unrecognized strings.
Accepts both lower- and upper-case unit suffixes used across the library
('1H'/'1h', '1D'/'1d', '1W'/'1w').
Map a resolution string to its interval in seconds. Returns
nullfor calendar-variable resolutions ('1M'months) where a fixed second-count would produce false gaps, and for unrecognized strings.Accepts both lower- and upper-case unit suffixes used across the library (
'1H'/'1h','1D'/'1d','1W'/'1w').