Performance: Avoid duplicate regex match in SuppressFilterElement.isFileMatch

I have read check documentation: https://checkstyle.org/filters/suppressionfilter.html
I have downloaded the latest cli from: https://checkstyle.org/cmdline.html#Download_and_Run
I have executed the cli and showed it below, as cli describes the problem better than 1,000 words

**How it works Now:**

```bash
/var/tmp $ javac Test.java

/var/tmp $ cat config.xml

/var/tmp $ tail -n 10 large-suppressions.xml

/var/tmp $ cat Test.java
public class Test {
public void foo() {}
}

/var/tmp $ RUN_LOCALE="-Duser.language=en -Duser.country=US"
/var/tmp $ java $RUN_LOCALE -jar checkstyle-10.21.4-all.jar -c config.xml Test.java
Starting audit...
Audit done.
```

**Is your feature request related to a problem? Please describe.**

We maintain a codebase with 10,000+ suppression entries generated for legacy files:

```xml

```

In a real project, we run Checkstyle through Maven across tens of thousands of files. When profiling Checkstyle
runs (inside the Maven Checkstyle Plugin), over 10 seconds was spent inside
[`SuppressFilterElement.isFileMatch`](https://github.com/checkstyle/checkstyle/blob/master/src/main/java/com/puppycrawl/tools/checkstyle/filters/SuppressFilterElement.java#L168-L175).

In `SuppressFilterElement.isFileMatch(String fileName)`:

```java
private boolean isFileMatch(String fileName) {
boolean match = fileRegexp.matcher(fileName).find();
if (!match) {
final String slashesFileName = fileName.replace('\\', '/');
match = fileRegexp.matcher(slashesFileName).find();
}
return match;
}
```

When a file path has no backslashes (`\`) (which is typical in our environments) `fileName.replace('\\', '/')`
returns the same string instance. Calling `fileRegexp.matcher(slashesFileName).find()`
again executes a duplicate regex.

I am proposing *a simple fix* that cuts the number of regex matches in half.

**Describe the solution you'd like**

Add a check (`slashesFileName != fileName`) to skip the second regex match when no substitution occurred:

```java
private boolean isFileMatch(String fileName) {
boolean match = fileRegexp.matcher(fileName).find();
if (!match) {
final String slashesFileName = fileName.replace('\\', '/');
if (slashesFileName != fileName) {
match = fileRegexp.matcher(slashesFileName).find();
}
}
return match;
}
```

Note that we don't need equals() as String.replace() returns the same instance when there's nothing to replace.

Start in src/main/java/com/puppycrawl/tools/checkstyle/filters/SuppressFilterElement.java and inspect isFileMatch(String fileName), using the supplied suppression configuration and CLI example to understand the current behavior. Ensure paths without backslashes do not trigger a duplicate regex match while slash normalization still works, then run the relevant filter tests if available.

Written by the indexing model from the issue text.