ament_clang_tidy corrupts Windows paths and diagnostic messages in xUnit output

## Description

`ament_clang_tidy` does not correctly parse clang-tidy diagnostics containing Windows absolute paths. The generated xUnit output contains a truncated file path and diagnostic message.

This affects xUnit reporting only; clang-tidy itself prints the diagnostic correctly.

## Environment

* Windows
* `ament_clang_tidy` 0.21.2 (Rolling)
* clang-tidy 19.1.7
* Python 3.12.3

## Reproduction

For example, clang-tidy reports:

```text
C:\pixi_ws\ros2-windows\include\rclcpp\rclcpp/any_subscription_callback.hpp:441:7: warning: 'set_deprecated>>' is deprecated: use 'void(std::shared_ptr)' instead [clang-diagnostic-deprecated-declarations]
```

Run `ament_clang_tidy` with xUnit output enabled:

```powershell
ament_clang_tidy.exe `
--xunit-file build\ament_clang_tidy.xunit.xml `
build\memfd_buffer_backend
```

The resulting xUnit contains:

```xml

/any_subscription_callback.hpp:441:7

```

## Expected

The xUnit result should preserve:

* the complete Windows path (`C:\...`)
* line and column
* the complete message following `warning:` or `error:`
* the associated diagnostic context in the failure body

## Cause

There appear to be three issues in `ament_clang_tidy/main.py`:

1. `error_re` assumes an absolute path starts with `/`:

```python
error_re = re.compile(
'(/.*?\\.(?:%s)):(\\d+):(\\d+): (?:warning:|error:)'
% '|'.join(extensions))
```

On Windows this starts matching at a later `/` in the path, dropping the drive and preceding directories.

2. `find_error_message()` uses the last colon in the line:

```python
def find_error_message(data):
return data[data.rfind(':') + 2:]
```

A diagnostic message can itself contain colons, e.g. `deprecated:` or `std::shared_ptr`, so this can truncate the message.

3. Diagnostic context is collected in `error['code_correct_rec']`, but `get_xunit_content()` checks the newly constructed `data` dictionary instead:

```python
if 'code_correct_rec' in data:
```

so the collected source lines and `note:` diagnostics are not included in the failure body.

### Did you use Generative AI?

Codex/Luna and ChatGPT were used for invetigation and creating the draft of this PR description.