Patch sysconfig data at install time (#9857)

## Summary

This PR reimplements
[`sysconfigpatcher`](https://github.com/bluss/sysconfigpatcher) in Rust
and applies it to our Python installations at install-time, ensuring
that the `sysconfig` data is more likely to be correct.

For now, we only rewrite prefixes (i.e., any path that starts with
`/install` gets rewritten to the correct absolute path for the current
machine).

Unlike `sysconfigpatcher`, this PR does not yet do any of the following:

- Patch `pkginfo` files.
- Change `clang` references to `cc`.

A few things that we should do as follow-ups, in my opinion:

1. Rewrite
[`AR`](https://github.com/bluss/sysconfigpatcher/blob/c1ebf8ab9274dcde255484d93ce0f1fd1f76a248/src/sysconfigpatcher.py#L61).
2. Remove `-isysroot`, which we already do for newer builds.

crates/uv-python/src/sysconfig/cursor.rs

@@ -0,0 +1,148 @@
+#![allow(dead_code)]
+
+use std::str::Chars;
+
+pub(super) const EOF_CHAR: char = '\0';
+
+/// A cursor represents a pointer in the source code.
+///
+/// Based on [`rustc`'s `Cursor`](https://github.com/rust-lang/rust/blob/d1b7355d3d7b4ead564dbecb1d240fcc74fff21b/compiler/rustc_lexer/src/cursor.rs)
+#[derive(Clone, Debug)]
+pub(super) struct Cursor<'src> {
+    /// An iterator over the [`char`]'s of the source code.
+    chars: Chars<'src>,
+
+    /// Stores the previous character for debug assertions.
+    #[cfg(debug_assertions)]
+    prev_char: char,
+}
+
+impl<'src> Cursor<'src> {
+    pub(super) fn new(source: &'src str) -> Self {
+        Self {
+            chars: source.chars(),
+            #[cfg(debug_assertions)]
+            prev_char: EOF_CHAR,
+        }
+    }
+
+    /// Returns the previous character. Useful for debug assertions.
+    #[cfg(debug_assertions)]
+    pub(super) const fn previous(&self) -> char {
+        self.prev_char
+    }
+
+    /// Peeks the next character from the input stream without consuming it.
+    /// Returns [`EOF_CHAR`] if the position is past the end of the file.
+    pub(super) fn first(&self) -> char {
+        self.chars.clone().next().unwrap_or(EOF_CHAR)
+    }
+
+    /// Peeks the second character from the input stream without consuming it.
+    /// Returns [`EOF_CHAR`] if the position is past the end of the file.
+    pub(super) fn second(&self) -> char {
+        let mut chars = self.chars.clone();
+        chars.next();
+        chars.next().unwrap_or(EOF_CHAR)
+    }
+
+    /// Returns the remaining text to lex.
+    ///
+    /// Use [`Cursor::text_len`] to get the length of the remaining text.
+    pub(super) fn rest(&self) -> &'src str {
+        self.chars.as_str()
+    }
+
+    /// Returns `true` if the cursor is at the end of file.
+    pub(super) fn is_eof(&self) -> bool {
+        self.chars.as_str().is_empty()
+    }
+
+    /// Moves the cursor to the next character, returning the previous character.
+    /// Returns [`None`] if there is no next character.
+    pub(super) fn bump(&mut self) -> Option<char> {
+        let prev = self.chars.next()?;
+
+        #[cfg(debug_assertions)]
+        {
+            self.prev_char = prev;
+        }
+
+        Some(prev)
+    }
+
+    pub(super) fn eat_char(&mut self, c: char) -> bool {
+        if self.first() == c {
+            self.bump();
+            true
+        } else {
+            false
+        }
+    }
+
+    pub(super) fn eat_char2(&mut self, c1: char, c2: char) -> bool {
+        let mut chars = self.chars.clone();
+        if chars.next() == Some(c1) && chars.next() == Some(c2) {
+            self.bump();
+            self.bump();
+            true
+        } else {
+            false
+        }
+    }
+
+    pub(super) fn eat_char3(&mut self, c1: char, c2: char, c3: char) -> bool {
+        let mut chars = self.chars.clone();
+        if chars.next() == Some(c1) && chars.next() == Some(c2) && chars.next() == Some(c3) {
+            self.bump();
+            self.bump();
+            self.bump();
+            true
+        } else {
+            false
+        }
+    }
+
+    pub(super) fn eat_if<F>(&mut self, mut predicate: F) -> Option<char>
+    where
+        F: FnMut(char) -> bool,
+    {
+        if predicate(self.first()) && !self.is_eof() {
+            self.bump()
+        } else {
+            None
+        }
+    }
+
+    /// Eats symbols while predicate returns true or until the end of file is reached.
+    #[inline]
+    pub(super) fn eat_while(&mut self, mut predicate: impl FnMut(char) -> bool) {
+        // It was tried making optimized version of this for eg. line comments, but
+        // LLVM can inline all of this and compile it down to fast iteration over bytes.
+        while predicate(self.first()) && !self.is_eof() {
+            self.bump();
+        }
+    }
+
+    /// Skips the next `count` bytes.
+    ///
+    /// ## Panics
+    ///  - If `count` is larger than the remaining bytes in the input stream.
+    ///  - If `count` indexes into a multi-byte character.
+    pub(super) fn skip_bytes(&mut self, count: usize) {
+        #[cfg(debug_assertions)]
+        {
+            self.prev_char = self.chars.as_str()[..count]
+                .chars()
+                .next_back()
+                .unwrap_or('\0');
+        }
+
+        self.chars = self.chars.as_str()[count..].chars();
+    }
+
+    /// Skips to the end of the input stream.
+    pub(super) fn skip_to_end(&mut self) {
+        self.chars = "".chars();
+    }
+}