Custom timescale

[valix25]

Is your feature request related to a problem? Please describe.

While the library is aimed at applications which require a calendar and time units like (seconds, hours, months etc.), there is a very good opportunity to make the library even more versatile by allowing a user to provide its own custom timescale. By this I mean that one can interpret the unix timestamps in a different way, as it is just a number it can represented as microseconds, nanoseconds etc. and from there one can build its own timescale with custom dividers multipliers.

Describe the solution you'd like
In terms of api, the user will provide the timescale multipliers and the labels for the given custom units. Some abstraction from dayjs and using plain number types will be required for flexibility. The default calendar timescale is preserved, unless the user provides its own timescale, at which point the library uses the provided timescale.

The issue will be referenced in a pull request to show how a custom timescale can be added in the library code.