account directives should disallow parentheses, square brackets

[simonmichael]

hledger's journal reader accepts but misparses parentheses/square brackets in account directives (reported by dentalfloss). Eg:

account (a)

2022-01-01
    a         0

$ hledger -f a.j accounts
(a)
a
$ hledger -f a.j check accounts
hledger: Error: /Users/simon/src/hledger/a.j:4:
  | 2022-01-01
4 |     a               0
  |     ^

Strict account checking is enabled, and
account "a" has not been declared.