new rule - useless if statement

ruff should be able to detect if the code on both sides of an if statement are identical, and report it as unnecessary
```py
if 1: # error: both sides of the if statement are the same
print(1)
else:
print(1)

asdf = 1 if bool() else 1 # error: both sides of the if expression are the same
```

No file or test is named in the issue. Start by locating Ruff's existing rules and tests for redundant branches or conditional expressions, then use both provided Python examples as regression cases; done means identical if branches and conditional-expression arms are reported as unnecessary.

Written by the indexing model from the issue text.