PR: Fix TimerObservable(==) comparing delay against itself

[docxology]

Closes: issue-01

Summary

getdelay_ms(t1) == getdelay_ms(t1) on the right-hand side of the second operand is a
copy-paste typo; the delay is never compared with t2. Fix the comparison to
getdelay_ms(t2).

Change

src/observable/timer.jl

# before
Base.:(==)(t1::TimerObservable, t2::TimerObservable) =
    getdelay_ms(t1) == getdelay_ms(t1) && getperiod_ms(t1) == getperiod_ms(t2)

# after
Base.:(==)(t1::TimerObservable, t2::TimerObservable) =
    getdelay_ms(t1) == getdelay_ms(t2) && getperiod_ms(t1) == getperiod_ms(t2)

How to verify

using Rocket, Test
@test TimerObservable(100.0, 50.0) != TimerObservable(999.0, 50.0)
@test TimerObservable(100.0, 50.0) == TimerObservable(100.0, 50.0)

Add the first assertion to test/observable/test_observable_timer.jl to lock it in.

Closes #69

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.42%. Comparing base (9ddfba9) to head (6d77a54).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
- Coverage   78.45%   78.42%   -0.03%     
==========================================
  Files         120      120              
  Lines        3829     3829              
==========================================
- Hits         3004     3003       -1     
- Misses        825      826       +1     

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[bvdmitri]

Maintainer note: added a regression test (test/observable/test_observable_timer.jl) asserting that timers differing only in delay are no longer equal. The original fix commit is unchanged. Held for you to merge once CI is green.