Update EUCAST expert rules versioning to month+year format

[msberends]

Summary

EUCAST expert rules have moved away from the numbered version scheme (last used: 3.3) to a month + year format (e.g., "January 2025"). The package needs to reflect this across all relevant files and functions.

Affected components

• data-raw/interpretive_rules.tsv — version identifiers stored in the data
• interpretive_rules() — the underlying function; version references in arguments, documentation, and logic
• eucast_rules() — the user-facing wrapper; same version references

Proposed behaviour

• Replace hard-coded version string "3.3" (and any other numbered versions) with the new month+year strings used by EUCAST
• When a user supplies a year only (e.g., "2026"), interpret it as the latest EUCAST expert rules up to and including that year — i.e., a convenient shorthand that selects the most recent applicable ruleset within that year
• Update documentation, argument descriptions, and any internal lookup/validation accordingly

References

• EUCAST expert rules page: https://www.eucast.org/expert_rules_and_expected_phenotypes