feat: add unit tests for some functionality as a starter

[yesudeep]

• Upgrades TypeScript compiler version
• Adds Jest for unit tests.
• Formats source code
• Adds alternative implementation for current formatting along with unit tests.

[yesudeep]

Unit test results:

~/code/github.com/yesudeep/viz-sankey-marketplace (add-sample-unit-tests)
fish❯ bin/test

changed 1 package in 803ms
yarn run v1.22.19
$ jest
 PASS  src/currency_formatter.test.ts
  fromSheetsToD3Format
    ✓ should sanitize the format correctly (3 ms)
    ✓ should return empty string when no value format provided unlike original implementation
  getCurrencySymbol
    ✓ should obtain the correct currency symbol
  getFormatSpan
    ✓ should obtain the span of the format if available (1 ms)
  getFormatSuffix
    ✓ should obtain the correct formatting suffix (1 ms)
  getGroupingSymbol
    ✓ should obtain the grouping delimiter (1 ms)

Test Suites: 1 passed, 1 total
Tests:       6 passed, 6 total
Snapshots:   0 total
Time:        2.002 s
Ran all test suites.
Done in 2.84s.

[tanyasingh1902]

LGTM