Support multi-file error enrichment using SourceFile

[LesterEvSe]

Since we will support modules, we need to know exactly where the error happened. Also, for single-file programs, nothing has changed, and the errors will be displayed the same way.

[KyrylR]

Suggested change

	pub fn with_file(self, file: Arc<str>) -> Self {
	pub fn with_file(self, program_content: Arc<str>) -> Self {

[KyrylR]

Add rust doc

[KyrylR]

Let's remove the comment

[KyrylR]

To avoid ambiguity with RichError, maybe it is better to have the following API shape:

• SourceFile { content: Arc<str>, name: Option<Arc<Path>> }
• RichError { error, span, source: Option<SourceFile> }
• parse_with_errors(source: &SourceFile, handler: &mut ErrorCollector)
• ErrorCollector::for_source(source.clone()) plus plain push/extend

Then clean up the API surface:

• Deprecate file(). It is ambiguous now (update the CHANGELOG.md)
• Replace file() it with explicit accessors like source_text(), source_name(), and maybe source()

[LesterEvSe]

• parse_with_errors(source: &SourceFile, handler: &mut ErrorCollector)

I did not change it because doing so could break the entire parser logic

[LesterEvSe]

• ErrorCollector::for_source(source.clone()) plus plain push/extend

The ErrorCollector::for_source(source.clone()) function is not needed because it is handled automatically inside the RichError::fmt(...) function