Add Scientific function set parity (trig, logs, combinatorics, stats basics, matrix ops)

## Goal
Reach core function parity for the Desmos scientific function surface.

## Scope
- Arithmetic/number: absolute value, percent, fraction input, nth root, factorial, round
- Constants: `pi`, `e`
- Trig: `sin`, `cos`, `tan`, `asin`, `acos`, `atan`
- Logs: `ln`, `log`
- Combinatorics: `nPr`, `nCr`
- Statistics (basic): `mean`, `stdev`, `stdevp`
- Matrix-related entries used in scientific flow:
- matrix template
- `rref`, `det`, `trace`, inverse, square, transpose

## Acceptance Criteria
- Each listed function/operator has parser support and evaluator support.
- Helpful errors are returned for invalid domains and malformed inputs.
- Function docs/examples exist in-project.
- Unit tests cover happy path and key edge cases for each category.