Add generic filtering mechanism

[jotaen]

This PR adds a new filter flag --filter to all evaluation commands, which accepts a generic filter query in the newly invented “klog filter language” format (KFL). E.g.:

• klog total --filter '2021-03-15 || #work' matches all entries that are either on 2021-03-15 or are tagged with #work.
• klog total --filter '2024-Q4 && (#work || #commute)' matches all entries of the fourth quarter of 2024 that either contain tags #work or #commute.
• klog total --filter '2022-01-15...2022-03-28' matches all entries from 2022-01-15 until 2022-03-28 (inclusive).

The KFL is basically a more generic version of the CLI’s built-in filter flags (--date, --tag, --period, etc.). While the built-in filter flags are AND’ed by default, KFL queries can combine the filter clauses with &&, ||, ! operators, and make use of grouping ((, )) with arbitrary nesting.

Todos

• Allow periods to appear in range clauses, e.g. 2020...2021-Q3 for all entries from the beginning of 2020 (2020-01-01) until the end of the third quarter of 2021 (2021-09-30).
• Attach position and length info directly to token type.
• For all parsing errors, ensure the error position and length is accurate.
• Sunset legacy service/query package and migrate to predicate mechanism.
• Write documentation (klog info --filtering).
• Decide on terminology – ideas:
  • KFL = klog filter language (maybe that sounds a bit too “big” for what it is)
  • KFE = klog filter expression
  • KFQ = klog filter query

References

Related #190.