Fix arguments passed to func callable in get_all_storage_variables

[BowTiedDevil]

Running slither-read-storage with the --variable-name argument results in an exception: TypeError: 'StateVariable' object is not subscriptable

Here is an example of reading the WETH balance for the Uniswap V4 PoolManager on mainnet:

(slither) btd@dev:~/code/slither_read_storage_fix$ slither-read-storage 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 --variable-name balanceOf --key 0x000000000004444c
5dc75cB358380D2e3dE08A90 --value --rpc-url http://localhost:8545
Traceback (most recent call last):
  File "/home/btd/code/slither_read_storage_fix/.venv/bin/slither-read-storage", line 10, in <module>
    sys.exit(main())
             ~~~~^^
  File "/home/btd/code/slither_read_storage_fix/slither/tools/read_storage/__main__.py", line 156, in main
    srs.get_all_storage_variables(lambda x: bool(x[1].name == args.variable_name))
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/btd/code/slither_read_storage_fix/slither/tools/read_storage/read_storage.py", line 400, in get_all_storage_variables
    if func(var):
       ~~~~^^^^^
  File "/home/btd/code/slither_read_storage_fix/slither/tools/read_storage/__main__.py", line 156, in <lambda>
    srs.get_all_storage_variables(lambda x: bool(x[1].name == args.variable_name))
                                                 ~^^^
TypeError: 'StateVariable' object is not subscriptable

The issue occurs because func is called within read_storage.py with a single argument var, but the lambda passed in the entrypoint expects a tuple:

if args.variable_name:
    # Use a lambda func to only return variables that have same name as target.
    # x is a tuple (`Contract`, `StateVariable`).
    srs.get_all_storage_variables(lambda x: bool(x[1].name == args.variable_name))
    srs.get_target_variables(**vars(args))
else:
    srs.get_all_storage_variables()
    srs.get_storage_layout()

This PR fixes the call by passing (contract, var) as the argument to func.

After fix:

(slither_read_storage_fix) btd@dev:~/code/slither_read_storage_fix$ slither-read-storage 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 --variable-name balanceOf --key 0x000000000004444c5dc75cB358380D2e3dE08A90 --value --rpc-url http://localhost:8545
INFO:Slither-read-storage:
Contract 'WETH9'
WETH9.balanceOf with type mapping(address => uint256) is located at slot: 3

INFO:Slither-read-storage:
Key: 0x000000000004444c5dc75cB358380D2e3dE08A90
Name: balanceOf
Type: uint256
Slot: 11839838417408005300668405460519842744078024714876931848523103724423050260794

INFO:Slither-read-storage:
Value: 22412870153270317898

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