Correct fractional-hour offset conversion and display

[OskarEichler]

Summary

Correct three offset arithmetic/sign errors affecting non-whole-hour timezones:

• Convert leftover seconds to minutes when rendering a numeric offset.
• Preserve the negative sign for a zero-hour offset such as -00:30.
• Display minutes, rather than remaining seconds, in EoTime#to_debug_s.

Reproduction

EtOrbi.get_tzone(19800) currently returns nil because the internal formatter produces "+05:1800"; it now resolves +05:30 with an offset of 19800 seconds. Both 5:30 and 5:45, positive/negative half-hour values, and zero were checked.

EtOrbi.get_tzone("-00:30") currently has a positive 1800-second offset; it now has -1800. Compact "-0030" was checked too.

EtOrbi::EoTime.new(0, "Asia/Kolkata").to_debug_s now contains "+05:30", not "+05:1800".

Verification

• Ruby 4.0.6 via rbenv; existing Probatio suite, no test files added or modified.
• Reviewed master baseline and this individual patch each run 270 tests / 412 assertions with exactly the same three pre-existing DST/rday failures from rday / rweek calculation is odd in time zones with DST #51. Failure identities were compared, not just counts.
• A release-based 1.4.1 branch containing the five separately proposed fixes passes 263 existing tests / 405 assertions with TZInfo 2.0.6 in UTC, Asia/Tokyo, America/Chicago, Europe/Istanbul and the detected local zone.
• Temporary focused before/after reproductions pass with TZInfo 2.0.6 and 1.2.11. The combined release branch also passes the existing TZInfo 1.2.11 suite at seed 36231. Seed 99751 has the same pre-existing Zulu test-order failure on both unmodified release and patched release: a test mutates the cached TZInfo object's comparison method.
• Ruby syntax and gem packaging checks pass. Targeted Lint passes on the combined branch with the existing, unrelated AssignmentInCondition warning excluded; no lint configuration was changed.

The current master's unreleased day-delta change was not brought into the consumer branch. No live scheduler or production operations were used. Linux/Windows and other Ruby runtimes were not run locally.

Breaking changes and limitations

No intended API break; malformed/reversed results become the correct offset. Existing whole-hour behavior is preserved. This does not expand the accepted hour range or add second-resolution numeric timezone support. Checked current source, open PRs and offset-related issues before publication.

[jmettraux]

Okay, so basically you decided to ruin my weekend.

[jmettraux]

What is this test wrecking crap?

[jmettraux]

Use assert instead of assert_equal. Do not remove the final blank line.

[OskarEichler]

Updated the regression to use the project assert style and restored the final blank line. The focused module suite passes with 156 tests and 232 assertions.

[jmettraux]

Enumerate the rules in the project assert style in a comment in this pull request.

[OskarEichler]

The project assertion rules I will follow are:

1. Use Probatio's assert, not Minitest's assert_equal.
2. With one ordinary argument, assert checks truthiness.
3. With one hash, it checks each key/value pair for equality.
4. With one regexp and one or more strings, it checks that the strings match.
5. Otherwise, it checks that all arguments are equal; in this repository the computed value is written first and the expected value second.
6. Preserve the surrounding test layout, including the blank line after a test opening and the final blank line in the file.

The current regression uses the two-argument equality form throughout, and c72d3de restores the final blank line. The focused module suite passes: 156 tests, 232 assertions.