fix: stop hashing the CSS class names

[TimG1804]

Closes #5.

postcss({ modules: true }) hashed the SCSS class names, so the bundled
stylesheet shipped

.squirrel-select_sqs-dropdown__wrapper__Re4RX
.squirrel-select_select__trigger__c0CbE
.squirrel-select_select__option__JQTYe

while the TypeScript adds the plain sqs-dropdown__wrapper,
select__trigger, select__option. src/index.ts imports the SCSS for its
side effect only and never reads the class map, so the two could never line
up — the injected stylesheet matched nothing and every consumer had to
write the whole thing themselves.

The names are already namespaced with sqs- and the README documents them
as the public styling API, so hashing them was never wanted here.

Verification

Built bundle before:

.squirrel-select_select__option__JQTYe
.squirrel-select_select__options__Ct12X
.squirrel-select_select__trigger__c0CbE
.squirrel-select_sqs-dropdown__wrapper__Re4RX

after:

.select  .selected  .select__option  .select__options
.select__trigger  .sqs-dropdown__wrapper  .open

which matches what DropdownCreation.ts and constantsAndHelpers.ts
assign. No hashed names remain in the output. eslint, tsc --noEmit and
rollup all run clean.

Not changed here: different-from-default-option and select__disabled
are applied by the TypeScript but have never existed in the stylesheet —
they are styling hooks for consumers, not a hashing problem.