fix(time): parse layouts like Go's time.Parse

[rcoreilly]

time.Parse and time.ParseInLocation were a stub built on the JS Date parser. They accepted values that do not match the layout (for example, "2025-05-15" parsed with RFC3339) and ignored the location for layouts like DateTime, using the host zone instead. github.com/BurntSushi/toml relies on Go's behavior: it tries a list of layouts in order and uses the first that parses, so the stub gave TOML dates and times the wrong type and value. ParseInLocation also did not accept a *Location held in a variable or struct field, which BurntSushi passes, so its parser failed to typecheck.

This replaces the stub with a port of Go's layout-driven parser from time/format.go: the same chunk tokenization, strict literal matching, fractional seconds (including implicit ones after the seconds field), numeric and named zones, day-of-year, range checks, and "extra text" errors, with ParseError messages that match Go's text. Zone offsets are matched against the given location, as in Go.

Related fixes in the same area:

• ParseInLocation now accepts Location, VarRef, or null, as Date and Time.In already do.
• ParseDuration is a port of Go's, so compound durations like "1m30s" and "-2h45m3.5s" parse. Its error messages now match Go's; one unit test expected "invalid duration" where Go reports "missing unit in duration", and is updated.
• Date builds values with setUTCFullYear/setFullYear. The Date constructors map years 0-99 to 1900-1999, which broke time-only layouts that parse to year 0.
• Format prints Z for any zero offset in the Z07:00 family, not only for the UTC location.
• Duration.String always prints seconds once a duration is at least one second, and prints minutes whenever there are hours ("1h30m0s"), as Go does.

The new fixtures package_import_time_parse_layout and package_import_time_parse_location_field cover BurntSushi's layouts with matching and non-matching values, error text, other layout elements, ParseDuration, and *Location struct fields. The full compiler suite, the gs/time unit tests, and typecheck pass.

[paralin]

Landed on master as 9439851. I folded package_import_time_parse_location_field into package_import_time_parse_layout. In parseTime, a local fail helper replaces the eight [new Time(), newParseError(alayout, avalue, ...)] returns, the time at a parsed offset is computed once, and the field declarations and result branches have paragraph comments. I also renamed parseBad and layoutChunk to PascalCase and shared one TextEncoder in quoteParseValue.