[vector_graphics_compiler] Fix HSL color parsing for decimal percentage components (#11619)

## Description

Fixes a bug in the HSL color parser where decimal percentage components
(e.g. `76.2745098039%`) were incorrectly multiplied by `2.55` — the
conversion factor used for **rgb** percentages (percent → 0–255).  For
**hsl**, saturation and lightness must stay in the 0–100 range (later
divided by 100) so the multiplication produced wildly wrong values
(e.g. `76.27 → 194`, then `194 / 100 = 1.94`).

The same branch also mis-handled the `hsla` alpha component: a unitless
decimal like `0.5` should be converted to 0–255 via `× 255`, not `× 2.55`.

### Root cause

`parser.dart` checked `rawColor.contains('.')` and unconditionally
applied `* 2.55`, regardless of whether the current function was
`rgb()`/`rgba()` (correct) or `hsl()`/`hsla()` (incorrect).

### Fix

Track whether each token had a `%` suffix before stripping it.
For HSL percentage components, return the raw `double` (0–100 range).
For unitless alpha decimals (0–1 range), multiply by 255.

### Reproduction (from issue #185833)

```
hsl(270, 100%, 76.2745098039%)
```

| Before fix | After fix |
|---|---|
| `#efdeff` ❌ | `#c286ff` ✓ |

## Tests

Four new tests added to `parsers_test.dart`:

- `hsl` with integer percentages (regression)
- `hsl` with decimal lightness percentage (the reported bug)
- `hsla` with integer percentages + decimal alpha (regression)
- `hsla` with decimal lightness + decimal alpha (combined case)

## Related Issues

Fixes https://github.com/flutter/flutter/issues/185833