imp: allow timestamp syntax in transaction dates

[Stealthmate]

This commit makes it possible to specify timestamps in hledger transactions. For example: 2024-01-01 12:43:56+09:00. All existing logic that uses the transaction's date information has been left unchanged - that is to say, the time of day is not used anywhere yet. The intention behind this is to modify such logic in future commits/pull requests.

Furthermore, backwards compatibility with existing ledgers using plain dates has been fully preserved (barring any bugs that I missed).

ref: #117

[simonmichael]

Thanks for this @Stealthmate. When you have a chance, rebase it and fix failing checks and I'll check it out.

[simonmichael]

Hi @Stealthmate. Do you have time to revisit this hledger PR: allow timestamp syntax in transaction dates ? It needs rebasing and test passing.

[simonmichael]

Closing for now.