[red-knot] Statically known branches (#15019)

## Summary

This changeset adds support for precise type-inference and
boundness-handling of definitions inside control-flow branches with
statically-known conditions, i.e. test-expressions whose truthiness we
can unambiguously infer as *always false* or *always true*.

This branch also includes:
- `sys.platform` support
- statically-known branches handling for Boolean expressions and while
  loops
- new `target-version` requirements in some Markdown tests which were
  now required due to the understanding of `sys.version_info` branches.

closes #12700 
closes #15034 

## Performance

### `tomllib`, -7%, needs to resolve one additional module (sys)

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `./red_knot_main --project /home/shark/tomllib` | 22.2 ± 1.3 | 19.1 |
25.6 | 1.00 |
| `./red_knot_feature --project /home/shark/tomllib` | 23.8 ± 1.6 | 20.8
| 28.6 | 1.07 ± 0.09 |

### `black`, -6%

| Command | Mean [ms] | Min [ms] | Max [ms] | Relative |
|:---|---:|---:|---:|---:|
| `./red_knot_main --project /home/shark/black` | 129.3 ± 5.1 | 119.0 |
137.8 | 1.00 |
| `./red_knot_feature --project /home/shark/black` | 136.5 ± 6.8 | 123.8
| 147.5 | 1.06 ± 0.07 |

## Test Plan

- New Markdown tests for the main feature in
  `statically-known-branches.md`
- New Markdown tests for `sys.platform`
- Adapted tests for `EllipsisType`, `Never`, etc

crates/red_knot_python_semantic/resources/mdtest/annotations/never.md

@@ -47,7 +47,9 @@ def f():
 
 ## `typing.Never`
 
-`typing.Never` is only available in Python 3.11 and later:
+`typing.Never` is only available in Python 3.11 and later.
+
+### Python 3.11
 
 ```toml
 [environment]
@@ -57,8 +59,17 @@ python-version = "3.11"
 ```py
 from typing import Never
 
-x: Never
+reveal_type(Never)  # revealed: typing.Never
+```
 
-def f():
-    reveal_type(x)  # revealed: Never
+### Python 3.10
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
+```py
+# error: [unresolved-import]
+from typing import Never
 ```

crates/red_knot_python_semantic/resources/mdtest/assignment/annotations.md

@@ -33,8 +33,6 @@ b: tuple[int] = (42,)
 c: tuple[str, int] = ("42", 42)
 d: tuple[tuple[str, str], tuple[int, int]] = (("foo", "foo"), (42, 42))
 e: tuple[str, ...] = ()
-# TODO: we should not emit this error
-# error: [call-possibly-unbound-method] "Method `__class_getitem__` of type `Literal[tuple]` is possibly unbound"
 f: tuple[str, *tuple[int, ...], bytes] = ("42", b"42")
 g: tuple[str, Unpack[tuple[int, ...]], bytes] = ("42", b"42")
 h: tuple[list[int], list[int]] = ([], [])

crates/red_knot_python_semantic/resources/mdtest/boolean/short_circuit.md

@@ -32,13 +32,10 @@ def _(flag: bool):
 
 ```py
 if True or (x := 1):
-    # TODO: infer that the second arm is never executed, and raise `unresolved-reference`.
-    # error: [possibly-unresolved-reference]
-    reveal_type(x)  # revealed: Literal[1]
+    # error: [unresolved-reference]
+    reveal_type(x)  # revealed: Unknown
 
 if True and (x := 1):
-    # TODO: infer that the second arm is always executed, do not raise a diagnostic
-    # error: [possibly-unresolved-reference]
     reveal_type(x)  # revealed: Literal[1]
 ```
 

crates/red_knot_python_semantic/resources/mdtest/call/callable_instance.md

@@ -67,6 +67,6 @@ def _(flag: bool):
             def __call__(self) -> int: ...
 
     a = NonCallable()
-    # error: "Object of type `Literal[__call__] | Literal[1]` is not callable (due to union element `Literal[1]`)"
-    reveal_type(a())  # revealed: int | Unknown
+    # error: "Object of type `Literal[1] | Literal[__call__]` is not callable (due to union element `Literal[1]`)"
+    reveal_type(a())  # revealed: Unknown | int
 ```

crates/red_knot_python_semantic/resources/mdtest/expression/if.md

@@ -7,7 +7,7 @@ def _(flag: bool):
     reveal_type(1 if flag else 2)  # revealed: Literal[1, 2]
 ```
 
-## Statically known branches
+## Statically known conditions in if-expressions
 
 ```py
 reveal_type(1 if True else 2)  # revealed: Literal[1]

crates/red_knot_python_semantic/resources/mdtest/literal/ellipsis.md

@@ -1,7 +1,23 @@
 # Ellipsis literals
 
-## Simple
+## Python 3.9
+
+```toml
+[environment]
+python-version = "3.9"
+```
+
+```py
+reveal_type(...)  # revealed: ellipsis
+```
+
+## Python 3.10
+
+```toml
+[environment]
+python-version = "3.10"
+```
 
 ```py
-reveal_type(...)  # revealed: EllipsisType | ellipsis
+reveal_type(...)  # revealed: EllipsisType
 ```

crates/red_knot_python_semantic/resources/mdtest/narrow/issubclass.md

@@ -95,10 +95,14 @@ def _(t: type[object]):
 
 ### Handling of `None`
 
+`types.NoneType` is only available in Python 3.10 and later:
+
+```toml
+[environment]
+python-version = "3.10"
+```
+
 ```py
-# TODO: this error should ideally go away once we (1) understand `sys.version_info` branches,
-# and (2) set the target Python version for this test to 3.10.
-# error: [possibly-unbound-import] "Member `NoneType` of module `types` is possibly unbound"
 from types import NoneType
 
 def _(flag: bool):