perf: improvements on the handling of amount

[jy95]

FHIR had reused many times these data structures across the Dosage object :

• Range
• Ratio

Let's make some cleanup in the handling

[codacy-production]

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Head commit (122f63e)	463 (+16)	463 (+16)	100.00% (+0.00%)

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	Coverable lines	Covered lines	Diff coverage
Pull request (#18)	68	68	100.00%

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[github-actions]

🎉 This PR is included in version 1.1.1 🎉

The release is available on:

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