Use Dates.yearmonthday function where appropriate

[adranka]

Use Dates.yearmonthday to simultaneously get the year, month, and day. This slightly improves performance:

Before:

julia> using BenchmarkTools

julia> using BusinessDays

julia> using Dates

julia> cal = BusinessDays.USSettlement();

julia> d = Date(2026, 1, 2);

julia> @btime isholiday($cal, $d);
  385.911 ns (0 allocations: 0 bytes)

julia> d = Date(2026, 1, 1);

julia> @btime isholiday($cal, $d);
  88.467 ns (0 allocations: 0 bytes)

After:

julia> d = Date(2026, 1, 2);

julia> @btime isholiday($cal, $d);
  348.192 ns (0 allocations: 0 bytes)

julia> d = Date(2026, 1, 1);

julia> @btime isholiday($cal, $d);
  50.441 ns (0 allocations: 0 bytes)

[felipenoris]

Awesome!