ENH copyright-notice: check in the first 4096 bytes instead of 1024 (#11927)

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## Summary
related to #5306

The check right now only checks in the first 1024 bytes, and that's
really not enough when there's a docstring at the beginning of a file.

A more proper fix might be needed, which might be more complex (and I
don't have the `rust` skills to implement that). But this temporary
"fix" might enable more users to use this.

Context: We want to use this rule in
https://github.com/scikit-learn/scikit-learn/ and we got blocked because
of this hardcoded rule (which TBH took us quite a while to figure out
why it was failing since it's not documented).

## Test Plan

This is already kinda tested, modified the test for the new byte number.

<!-- How was it tested? -->

Author: adrinjalali

crates/ruff_linter/src/rules/flake8_copyright/mod.rs

@@ -295,6 +295,36 @@ import os
 # Content Content Content Content Content Content Content Content Content Content
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 # Copyright 2023
 "

crates/ruff_linter/src/rules/flake8_copyright/rules/missing_copyright_notice.rs

@@ -8,6 +8,8 @@ use crate::settings::LinterSettings;
 /// ## What it does
 /// Checks for the absence of copyright notices within Python files.
 ///
+/// Note that this check only searches within the first 4096 bytes of the file.
+///
 /// ## Why is this bad?
 /// In some codebases, it's common to have a license header at the top of every
 /// file. This rule ensures that the license header is present.
@@ -31,8 +33,8 @@ pub(crate) fn missing_copyright_notice(
         return None;
     }
 
-    // Only search the first 1024 bytes in the file.
-    let contents = locator.up_to(locator.floor_char_boundary(TextSize::new(1024)));
+    // Only search the first 4096 bytes in the file.
+    let contents = locator.up_to(locator.floor_char_boundary(TextSize::new(4096)));
 
     // Locate the copyright notice.
     if let Some(match_) = settings.flake8_copyright.notice_rgx.find(contents) {