Release 0.9.11 "Prayer" - Uncertain number

This release implements arithmetic and basic functions on uncertain numbers.
This propagates uncertainty using quadradic superposition, in a way similar to
OpenRPNCalc, with a generalization for correlated variables.

New features
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* Arithmetic and basic functions on uncertain numbers
* Add support for complex-valued unit objects, e.g. `5+3ⅈ Ω`
* Add support for range-valued unit objects, e.g. `1…3 Ω`
* Support arithmetic operation on infinities, e.g. `∞ 42 +`
* Add commands to generate mathematical constants (π, ℮, ∞ and −∞)
* Parsing and editing of ranges containing infinities
* Accept infinities in `→Range` and variants
* Comparison of infinite values and finite values
* Add union and intersection commands for ranges
* Add operations to build ranges and uncertain numbers from components
* Add derivative for `erf` and `erfc`

Bug fixes
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* Do not leave bad expressions behind after errors on ranges
* Obey the `InfinityError` flag when detecting divide-by-zero in ranges
* Avoid crash pushing null pointer after unit evaluation error
* Avoid spurious inconsistent units error due to date computations
* Null-protection in variadic `list::make`, fixes null-deref crash

Improvements
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* Accelerate error exit from arithmetic operations
* Render uncertain numbers as `110±σ15` instead of `110±15σ`
* Accept `−` as valid input in constants (for `−∞`)
* Record performance data for iPhone 16
* Change spelling to `→σRange` in `RangeMenu`
* Use `ASSERT` for divide by zero inner checks (remove dead code)

Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>