fix: check whether the parsed time contains timezone

[yuankunzhang]

Closes #147.

Why m1y was accepted: m1y was parsed as an offset m and a time 1y; the time 1y contains two elements: the hour 1 and the offset y. So the problem here is the duplication of offsets.

cc @drinkcat

[drinkcat]

Thanks! LGTM. Found this easier to review by looking at the individual commits.

[sylvestre]

---- tests::iso_8601::test_space_sep stdout ----
thread 'tests::iso_8601::test_space_sep' panicked at 'assertion failed: `(left == right)`
  left: `1613389067`,
 right: `1613371067`', src/lib.rs:139:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[yuankunzhang]

Hi @cakebaker , please help review this PR, thanks.

[cakebaker]

Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (1a6a6f6) to head (3fe06c0).
Report is 4 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff     @@
##   main   #150   +/-   ##
===========================
===========================

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