limit TimeType subtraction

[JeffBezanson]

Implements the plan approved by triage. Replaces #49805.

[KristofferC]

Isn't this a bit breaking? From PkgEval on backport branch:

Error During Test at /home/pkgeval/.julia/packages/MonthlyDates/dqXkG/test/runtests.jl:75
  Test threw exception
  Expression: MonthlyDate(1990, 1) - MonthlyDate(1989, 1) == Month(12)
  MethodError: no method matching -(::MonthlyDate, ::MonthlyDate)

     accessors: Error During Test at /home/pkgeval/.julia/packages/Intervals/V53WF/test/interval.jl:128
  Test threw exception
  Expression: span(interval) == b - a
  MethodError: no method matching -(::InfExtendedTime{Date}, ::InfExtendedTime{Date})

Test threw exception
Expression: !(l1 in dr)
MethodError: no method matching -(::QDates.QDate, ::QDates.QDate)

Closest candidates are:
  -(::QDates.QDate, !Matched::Dates.CompoundPeriod)
    @ QDates ~/.julia/packages/QDates/Zu2GK/src/periods.jl:14
  -(::QDates.QDate, !Matched::Dates.Year)

  Testing Running tests...
  arithmetic: Error During Test at /home/pkgeval/.julia/packages/UnixTimes/pJJGK/test/runtests.jl:63
    Test threw exception
    Expression: UnixTime(2020, 1, 1, 10) - UnixTime(2020, 1, 1, 9) == Nanosecond(60 * 60 * 1000000000)
    StackOverflowError:
    Stacktrace:
      [1] -(x::UnixTime, y::UnixTime) (repeats 79984 times)
        @ Dates /opt/julia/share/julia/stdlib/v1.10/Dates/src/arithmetic.jl:12

     Testing Running tests...
ERROR: LoadError: MethodError: no method matching -(::SemesterDate, ::SemesterDate)

Closest candidates are:
  -(::SemesterDate, !Matched::Year)
   @ ExtendedDates ~/.julia/packages/ExtendedDates/ibFpe/src/arithmetic.jl:23
  -(::SemesterDate, !Matched::Semester)
   @ ExtendedDates ~/.julia/packages/ExtendedDates/ibFpe/src/arithmetic.jl:35