Add string parsing, humanize(), many unit families, and Laravel integration

[khaledalam]

Builds out the four most-requested capabilities to make the library more useful and broaden its reach.

Added

• String parsing — Quantity::parse('100 km/h'), Quantity::parse('-40 °C'), and multi-segment Quantity::parse('5 ft 3 in') (same-dimension segments are summed).
• Quantity::humanize() — auto-selects the most readable unit via curated ladders (1500 m → 1.5 km, 2_500_000 B → 2.5 MB), leaving affine temperature units untouched.
• Many more unit families — speed, data (decimal + binary), force, energy, power, pressure, frequency, angle, plus more length/mass/time/area/volume units. All verified against known reference values.
• Laravel integration — auto-discovered UnitServiceProvider and an Eloquent AsQuantity cast (store a quantity in one column, get a Quantity back; strings are parsed on write). Custom units via config/unit.php.

Notes

• illuminate/database added to require-dev (+ suggest); the Laravel test skips cleanly when it's absent.
• PHPStan stays at level max, clean; the extended dimension model (data B, angle A) is fully typed.

Verification

• 21/21 tests pass (incl. Eloquent cast round-trip), PHPStan max clean, CS-Fixer clean.
• Live demo (docs/) extended with all new families; conversion math cross-checked against the PHP library.