Make scheme a cached property as well

[bdraco]

Noticed this one comes up a lot while profiling #1039

What do these changes do?

Make scheme a cached property as well

Are there changes in behavior for the user?

No

This likely makes very little difference, but we might as well include it since we use @cached_property for any immutable property we access more than once. Once we can use the cython version per #1065 this will be a bit faster.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.60%. Comparing base (e3dd736) to head (42bca26).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1058   +/-   ##
=======================================
  Coverage   62.60%   62.60%           
=======================================
  Files          38       38           
  Lines        6721     6721           
  Branches      368      368           
=======================================
  Hits         4208     4208           
  Misses       2486     2486           
  Partials       27       27           

Flag	Coverage Δ
CI-GHA	62.57% <100.00%> (ø)
MyPy	25.92% <100.00%> (+0.01%)	⬆️
OS-Linux	99.26% <100.00%> (ø)
OS-Windows	99.59% <100.00%> (ø)
OS-macOS	99.03% <100.00%> (ø)
Py-3.10.11	98.94% <100.00%> (ø)
Py-3.10.14	99.15% <100.00%> (ø)
Py-3.11.9	99.15% <100.00%> (ø)
Py-3.12.5	99.15% <100.00%> (ø)
Py-3.13.0-rc.1	99.15% <100.00%> (ø)
Py-3.8.10	98.88% <100.00%> (ø)
Py-3.8.18	99.09% <100.00%> (ø)
Py-3.9.13	98.88% <100.00%> (ø)
Py-3.9.19	99.09% <100.00%> (ø)
Py-pypy7.3.11	99.40% <100.00%> (ø)
Py-pypy7.3.16	99.43% <100.00%> (ø)
VM-macos-latest	99.03% <100.00%> (ø)
VM-ubuntu-latest	99.26% <100.00%> (ø)
VM-windows-latest	99.59% <100.00%> (ø)

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