[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/src/module_resolver/resolver.rs

@@ -721,8 +721,8 @@ mod tests {
     use crate::module_name::ModuleName;
     use crate::module_resolver::module::ModuleKind;
     use crate::module_resolver::testing::{FileSpec, MockedTypeshed, TestCase, TestCaseBuilder};
-    use crate::ProgramSettings;
     use crate::PythonVersion;
+    use crate::{ProgramSettings, PythonPlatform};
 
     use super::*;
 
@@ -1262,7 +1262,7 @@ mod tests {
     fn symlink() -> anyhow::Result<()> {
         use anyhow::Context;
 
-        use crate::program::Program;
+        use crate::{program::Program, PythonPlatform};
         use ruff_db::system::{OsSystem, SystemPath};
 
         use crate::db::tests::TestDb;
@@ -1296,6 +1296,7 @@ mod tests {
             &db,
             &ProgramSettings {
                 python_version: PythonVersion::PY38,
+                python_platform: PythonPlatform::default(),
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: src.clone(),
@@ -1801,6 +1802,7 @@ not_a_directory
             &db,
             &ProgramSettings {
                 python_version: PythonVersion::default(),
+                python_platform: PythonPlatform::default(),
                 search_paths: SearchPathSettings {
                     extra_paths: vec![],
                     src_root: SystemPathBuf::from("/src"),