Fix apiVersion type inconsistency - ensure consistent number return type

[Copilot]

Fixed a type inconsistency bug where apiVersion was returned as different types depending on the source:

Problem:

• When apiVersion was extracted from Accept header via regex match, it returned a string (e.g., '1')
• When apiVersion came from defaultVersion option, it returned a number (e.g., 1)
• This inconsistency could cause issues in applications using strict type checking

Example of the issue:

const requestVersion = require('@cmsgov/qpp-shared-api-versioning-node');

// Case 1: From Accept header - returned STRING
const req1 = { headers: { accept: 'application/vnd.qpp.cms.gov.v1+json' } };
requestVersion.setVersion()(req1, {}, () => {});
console.log(typeof req1.apiVersion); // "string" (was inconsistent)

// Case 2: From defaultVersion - returned NUMBER  
const req2 = { headers: {} };
requestVersion.setVersion({ defaultVersion: 1 })(req2, {}, () => {});
console.log(typeof req2.apiVersion); // "number" (always consistent)

Solution:

• Modified index.js line 36 to use parseInt(version) instead of version
• Now apiVersion consistently returns a number in both scenarios
• Added focused test with assert.strictEqual() to prevent regression

Impact:

• All existing tests pass (18/18)
• Backward compatible - existing code using loose equality (==) continues to work
• Improves reliability for applications using strict equality (===) or TypeScript

Fixes #33.

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