Compute real 1D FFT for 1D arrays with two complex FFTs when possible

[andreasnoack]

Also, compute the real 1D FFT of ND arrays with mapslices to avoid code duplication.

I have added comments in the code to explain the approach. With the changes here
we go from

julia> @btime irfft(rfft(xx), 2^11) setup=(xx=randn(2^11));
  41.875 μs (46 allocations: 197.64 KiB)

to

julia> @btime irfft(rfft(xx), 2^11) setup=(xx=randn(2^11));
  19.916 μs (34 allocations: 69.39 KiB)

I hope to do something similar for the 2D case, but it requires some more thinking on my side to get things right.

[codecov]

Codecov Report

❌ Patch coverage is 94.59459% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.24%. Comparing base (214407d) to head (c266455).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/plan.jl	94.59%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #98      +/-   ##
==========================================
- Coverage   97.96%   97.24%   -0.73%     
==========================================
  Files           4        4              
  Lines         393      435      +42     
==========================================
+ Hits          385      423      +38     
- Misses          8       12       +4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[andreasnoack]

For visibility, here is the current main

and here is this PR

@dannys4 I have added a commit where I bump the version number as I'd like to benefit from this downstream. Are you okay with a new release?

[dannys4]

forgot to respond but yeah version bumping is always fine with me