separate boundary grad and value extrapolation, make grad default quadratic #11119

Job	Run time
Doctests (ubuntu-latest / Python 3.11)	3m 44s
Example notebooks (ubuntu-latest / Python 3.12)	19m 34s
Example scripts (ubuntu-latest / Python 3.12)	13m 1s
style	23s
Tests (ubuntu-latest / Python 3.9)	30m 53s
Tests (ubuntu-latest / Python 3.10)	29m 45s
Tests (ubuntu-latest / Python 3.11)	27m 51s
Tests (ubuntu-latest / Python 3.12)	32m 32s
Tests (macos-13 / Python 3.9)	26m 38s
Tests (macos-13 / Python 3.10)	39m 27s
Tests (macos-13 / Python 3.11)	29m 17s
Tests (macos-13 / Python 3.12)	24m 11s
Tests (macos-14 / Python 3.9)	12m 57s
Tests (macos-14 / Python 3.10)	10m 48s
Tests (macos-14 / Python 3.11)	10m 58s
Tests (macos-14 / Python 3.12)	9m 22s
Tests (windows-latest / Python 3.9)	32m 59s
Tests (windows-latest / Python 3.10)	31m 17s
Tests (windows-latest / Python 3.11)	30m 18s
Tests (windows-latest / Python 3.12)	29m 7s
	7h 25m 2s

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