fix: make exact-match whitespace collapsing opt-out

[slegarraga]

Closes #9.

Adds a collapseWhitespace option to normalize() and threads it through exactMatchScorer.

• collapseWhitespace defaults to true, preserving current behavior
• setting it to false (with caseSensitive: true and trim: false) enables a byte-exact comparison
• README and scorer docs now list the option
• regression tests cover internal whitespace collapsing on and off

Verified with npm run typecheck and npm test (69 passed).

[royalpinto007]

Closing this PR.

The author is no longer an active contributor on these repositories, so this cannot be carried through review or iterated on.

The underlying issue stays open and is available for anyone who wants it. If you were looking at this change, please do open a fresh PR, it is very welcome.