refactor: replace shannonToCKB with lumos formatUnit

[twhy]

How this PR was implemented

1. Rewrite shannonToCKB with @ckb-lumos/bi/formatUnit as below.

import { formatUnit, ckbDecimals } from '@ckb-lumos/bi'

const shannonToCKB = (shannon: bigint) => {
  return new Intl.NumberFormat('en-US', {
    useGrouping: false,
    signDisplay: 'always',
    minimumFractionDigits: ckbDecimals,
    maximumFractionDigits: ckbDecimals,
  }).format(Number(formatUnit(shannon, 'ckb')))
}

export default shannonToCKB

2. Run shannonToCKB.test.ts to make sure the new implementation pass all tests.

3. Go to to-csv-row.ts(the only file using shannonToCKB), rewrite

amount = shannonToCKB(BigInt(tx.value ?? ''))

as

amount = new Intl.NumberFormat('en-US', {
  useGrouping: false,
  signDisplay: 'always',
  minimumFractionDigits: ckbDecimals,
  maximumFractionDigits: ckbDecimals,
}).format(Number(formatUnit(BigInt(tx.value ?? '0'), 'ckb'))) 

BigInt('') and BigInt('0') are both evaluated to 0n, but BigInt('0') is more explicit.

4. Delete shannonToCKB.ts and shannonToCKB.test.ts

[homura]

Looks good. Since version 0.22, Lumos has provided an entry package @ckb-lumos/lumos that includes almost all common functions. It's suggested to import only @ckb-lumos/lumos for more convenience

import { formatUnit } from '@ckb-lumos/lumos/utils'
formatUnit(...)

// or
import { utils } from '@ckb-lumos/lumos'
utils.formatUnit(...)

[twhy]

@homura That's very convinient!

But the neuron-wallet is still using 0.21.1
https://github.com/nervosnetwork/neuron/blob/develop/packages/neuron-wallet/package.json#L45

Also, the lumos package has not exported ckbDecimals
https://github.com/ckb-js/lumos/blob/develop/packages/lumos/src/utils.ts#L10

So to keep this PR simple, we probably should create a separate PR to upgrade the lumos dependencies and update the imports after this one get merged.