Eliminate allocation with ZonedDateTime constructor using is_dst::Bool

[omus]

Fixes #495. We now no longer see allocations when using ZonedDateTime(dt, tz, is_dst::Bool) when the local date/time is not ambiguous. We still see allocations when it is ambiguous though.

julia> VERSION
v"1.12.2"

julia> @allocated ZonedDateTime(DateTime(2025, 7, 18, 22, 5), tz"Europe/Berlin", true)  # unambiguous
0

julia> @allocated ZonedDateTime(DateTime(2025, 10, 26, 2), tz"Europe/Berlin", 1)  # ambiguous
0

julia> @allocated ZonedDateTime(DateTime(2025, 10, 26, 2), tz"Europe/Berlin", 2) # ambiguous
0

julia> @allocated ZonedDateTime(DateTime(2025, 10, 26, 2), tz"Europe/Berlin", true) # ambiguous
64

julia> @allocated ZonedDateTime(DateTime(2025, 10, 26, 2), tz"Europe/Berlin", false) # ambiguous
64

[omus]

Julia 1.10.10, 1.11.7, 1.12.2, and 1.14.0-DEV.1310 all report this on the REPL:

julia> @allocated ZonedDateTime(DateTime(2025, 7, 18, 22, 5), tz"Europe/Berlin", true)
0

I'm not sure why I see allocations in the tests on Julia 1.12.2 and 1.14.0-DEV.1310 but this overall seems like an improvement.

[omus]

Turns out I didn't need this after all

[giordano]

I'm not sure why I see allocations in the tests on Julia 1.12.2 and 1.14.0-DEV.1310 but this overall seems like an improvement.

Code coverage is effectful and in v1.12+ it tends to cause extra allocations.

[omus]

I'm not sure why I see allocations in the tests on Julia 1.12.2 and 1.14.0-DEV.1310 but this overall seems like an improvement.

Code coverage is effectful and in v1.12+ it tends to cause extra allocations.

Good to know. That may not be the root cause here though since Pkg.test(coverage=true) and Pkg.test(coverage=false) have the same allocations.