fix: count days in duration parser

[KaisAbiyyi]

Closes #1

Summary:

• Adds the missing d unit to the duration unit table so day values are counted as 86400 seconds.
• Adds regression coverage for 1d, 2d4h, and an all-unit combined duration string.
• Updates the README example so the documented d support has a visible working example.

Comparison with existing submissions:

• Recent PRs such as fix: add days (d) unit support to parse_duration #51 and fix: add days (d) unit support to parse_duration (fixes #1) #52 add the missing unit and tests.
• This PR keeps the same focused fix, adds the full supported-unit regression case, and updates README usage coverage so the documented day unit is represented in examples too.

Demo:

• Short demo video (MP4)

Verification:

• python -m unittest discover -s tests
• manual check: 1d -> 86400, 2d4h -> 187200, 1w2d3h4m5s -> 788645
• git diff --check

Bounty context: resolves the $50 Algora bounty on #1.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds support for parsing days (d) in duration strings across implementation, tests, and documentation.

Changes:

• Add d (days) to supported duration units in duration_utils.py
• Expand unit parsing tests to cover days and multi-unit combinations
• Update README usage examples to include day-based durations

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tests/test_duration_utils.py	Adds coverage for parsing d and mixed unit strings including w+d+h+m+s.
duration_utils.py	Extends _UNITS with days and documents an additional example.
README.md	Documents d usage through an added example call.

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