feat: add policy composable

[brc-dd]

closes #419

Usage:

import {
  type Policy,
  type PolicyResponse,
  type PolicyHelpers as SefirotPolicyHelpers,
  usePolicy as sefirotUsePolicy
} from 'sefirot/composables/Policy'

interface PolicyHelpers<Code extends string | undefined = undefined>
  extends SefirotPolicyHelpers<Code> {
  user: { admin: boolean }
}

function usePolicy<Code extends string | undefined = undefined>(
  fn: (helpers: PolicyHelpers<Code>) => PolicyResponse<Code>
): Policy<Code> {
  const user = { admin: true }

  return sefirotUsePolicy((helpers) => {
    return fn({ ...helpers, user })
  })
}

// ...

import { type Policy, usePolicy } from './Policy'

function canDoFoo(): Policy<'foo' | 'bar'> {
  return usePolicy(({ user, allow, deny }) => {
    return user.admin ? allow('foo') : deny('bar')
  })
}

function canDoBar(): Policy {
  return usePolicy(({ user, allow, deny }) => {
    return user.admin ? allow() : deny()
  })
}

// alternatively

import { usePolicy } from './Policy'

export function canDoFoo() {
  return usePolicy<'foo' | 'bar'>(({ user, allow, deny }) => {
    return user.admin ? allow('foo') : deny('bar')
  })
}

export function canDoBar() {
  return usePolicy(({ user, allow, deny }) => {
    return user.admin ? allow() : deny()
  })
}

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