add bitcoin utils

backend/src/consts/btcAtomicPerBtc.ts

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+import Decimal from 'decimal.js';
+
+export const BTC_ATOMIC_PER_BTC = new Decimal(100_000_000);

backend/src/types/BitcoinConfirmationTier.ts

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+export interface BitcoinConfirmationTier {
+    upToTotalFiat?: string;
+    minConfirmations: number;
+}

backend/src/utils/bitcoin/convertBtcAtomicToBtc.spec.ts

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+import { convertBtcAtomicToBtc } from './convertBtcAtomicToBtc';
+
+describe('convertBtcAtomicToBtc', () => {
+    it('converts atomic units to BTC', () => {
+        expect(convertBtcAtomicToBtc('100000000')).toBe('1.00000000');
+    });
+
+    it('converts a single atomic unit to BTC', () => {
+        expect(convertBtcAtomicToBtc('1')).toBe('0.00000001');
+    });
+});

backend/src/utils/bitcoin/convertBtcAtomicToBtc.ts

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+import Decimal from 'decimal.js';
+import { BTC_ATOMIC_PER_BTC } from '../../consts/btcAtomicPerBtc';
+
+export const convertBtcAtomicToBtc = (
+    amountAtomic: string,
+    rounding: Decimal.Rounding = Decimal.ROUND_HALF_UP
+): string => {
+    return new Decimal(amountAtomic).div(BTC_ATOMIC_PER_BTC).toDecimalPlaces(8, rounding).toFixed(8);
+};

backend/src/utils/bitcoin/convertBtcToBtcAtomic.spec.ts

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+import { convertBtcToBtcAtomic } from './convertBtcToBtcAtomic';
+
+describe('convertBtcToBtcAtomic', () => {
+    it('converts one BTC to atomic units', () => {
+        expect(convertBtcToBtcAtomic('1')).toBe('100000000');
+    });
+
+    it('converts the smallest display unit to atomic units', () => {
+        expect(convertBtcToBtcAtomic('0.00000001')).toBe('1');
+    });
+
+    it('returns an integer string without scientific notation', () => {
+        expect(convertBtcToBtcAtomic('0.00125907')).toBe('125907');
+        expect(convertBtcToBtcAtomic('0.00125907')).not.toMatch(/e/i);
+    });
+});

backend/src/utils/bitcoin/convertBtcToBtcAtomic.ts

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+import Decimal from 'decimal.js';
+import { BTC_ATOMIC_PER_BTC } from '../../consts/btcAtomicPerBtc';
+
+export const convertBtcToBtcAtomic = (amountBtc: string): string => {
+    return new Decimal(amountBtc).mul(BTC_ATOMIC_PER_BTC).toDecimalPlaces(0, Decimal.ROUND_HALF_UP).toString();
+};

backend/src/utils/bitcoin/convertFiatToBtc.spec.ts

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+import { convertFiatToBtc } from './convertFiatToBtc';
+
+describe('convertFiatToBtc', () => {
+    it('formats small amounts without scientific notation', () => {
+        expect(convertFiatToBtc(0.01, 100_000)).toBe('0.00000010');
+    });
+
+    it('converts fiat to BTC at the shop rate', () => {
+        expect(convertFiatToBtc(50_000, 100_000)).toBe('0.50000000');
+    });
+});

backend/src/utils/bitcoin/convertFiatToBtc.ts

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+import Decimal from 'decimal.js';
+
+export const convertFiatToBtc = (fiatAmount: number, fiatPerBtc: number): string => {
+    return new Decimal(fiatAmount).div(fiatPerBtc).toDecimalPlaces(8, Decimal.ROUND_HALF_UP).toFixed(8);
+};