📝 SafeTransferLib: `checkBalanceOf` NatSpec for `implemented` return value is inverted

[BhariGowda]

Summary

The NatSpec for checkBalanceOf describes the implemented return value
incorrectly — the description is semantically inverted relative to the actual
code behavior.

Current NatSpec (line 458)

/// `implemented` denotes whether the `token` does not implement `balanceOf`.

Actual behavior

implemented := and(
    gt(returndatasize(), 0x1f),
    staticcall(gas(), token, 0x10, 0x24, 0x20, 0x20)
)

staticcall returns 1 on success. implemented is therefore true when the
call succeeds — i.e., when the token does implement balanceOf.

The word "not" in the NatSpec inverts the meaning. A developer reading the docs
would expect implemented == true to mean "token lacks balanceOf", but the
opposite is true.

Suggested fix

/// `implemented` is `true` if the `token` implements `balanceOf`, `false` otherwise.
/// `amount` is zero if the `token` does not implement `balanceOf`.

[atarpara]

fixed at #1531