feat: add META symbol to exports

[lukekarrys]

Two things to note:

• The key is the string 'META'
• The value is Symbol('proc-log.meta')

So it could be used like the following. All of the following is up to producers/consumers to implement with shared conventions. All proc-log is doing to allowing them to share a unique Symbol.

const { output, META } = require('../')

// An example of how consumers would see if a META object
// was the last argument from an event
const getMeta = (args) => {
  let meta = {}
  const last = args.at(-1)
  if (last && typeof last === 'object' && Object.hasOwn(last, META)) {
    meta = args.pop()
  }
  return [meta, ...args]
}

process.on('output', (level, ...rawArgs) => {
  const [{ force = false }, ...args] = getMeta(rawArgs)
  console.log(level, { force, args })
})

// in this implementation the value does not matter, just the key
output.standard('arg1', 'arg2', { [META]: null, force: true })
output.standard('arg1', 'arg2')
output.standard('arg1', null)
output.standard(null)
output.standard()

// Will log the following:
// standard { force: true, args: [ 'arg1', 'arg2' ] }
// standard { force: false, args: [ 'arg1', 'arg2' ] }
// standard { force: false, args: [ 'arg1', null ] }
// standard { force: false, args: [ null ] }
// standard { force: false, args: [] }

Closes: #81

[wraithgar]

This only works if we have one proc-log in the tree.