Replace chrono with jiff for date/time handling (Closes #178)

[octoaide]

Closes #178

This pull request replaces the chrono crate with jiff for all date and time handling throughout the codebase.

Motivation

jiff is a better-maintained library that provides a more modern and robust approach to date/time handling in Rust compared to chrono. This migration improves the long-term maintainability and reliability of our date/time operations.

Summary of Changes

• Added jiff as a dependency, including the serde feature.
• Removed chrono as a dependency from Cargo.toml.
• Migrated all usages of chrono to jiff in src/stats.rs, src/table.rs, and src/csv/reader.rs.
• Updated date/time parsing, formatting, and manipulation logic to use jiff's API, including:
  • chrono::NaiveDateTime replaced with jiff::civil::DateTime
  • NaiveDate::from_ymd_opt().and_hms_opt() -> date().at()
  • DateTime::from_timestamp() -> jiff::Timestamp::from_second()
  • .and_utc().timestamp_nanos_opt() -> .to_zoned(TimeZone::UTC).timestamp().as_nanosecond()
  • chrono::format::ParseError -> jiff::Error
  • .format() -> .strftime()
• Updated all relevant unit tests to reflect the jiff API.
• Added an entry to CHANGELOG.md documenting this dependency switch.
• Confirmed all tests pass and no new clippy warnings are introduced.

This change ensures that functionality remains fully backward compatible while leveraging the benefits of jiff.