Fix test errors and date/time loading from epoch

[theit8514]

Two test fixes:

1. Exclude .md files from test run and coverage, fixes parse errors on pnpm run test.
2. On my local machine (UTC-4), the date/time unit test fails due to epoch being processed as local time instead of UTC.

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 FAIL  src/tests/util/date.test.ts > Util: date > dateStringFromEpoch > validates standard formatting, custom patterns, and edge cases
AssertionError: expected '1969-12-31' to be '1970-01-01' // Object.is equality

Expected: "1970-01-01"
Received: "1969-12-31"

 ❯ src/tests/util/date.test.ts:103:35
    101|
    102|    // Unix Epoch start
    103|    expect(dateStringFromEpoch(0)).toBe("1970-01-01");
       |                                   ^
    104|
    105|    // Negative epoch (pre-1970)

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Instead of changing the test, I have updated the dateStringFromEpoch to load from UTC instead of local. This will cause the charts to shift their visible X axis labels by 1 day.

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[codacy-production]

Up to standards ✅

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