[Storage] Proposed HttpRange generated model proof-of-concept

[vincenttran-msft]

Currently when a range is specified, it must be in a specific format, and so we provided the format_page_range() function. Looking closer, this seems to be a common issue with any time range is specified, and we want to align with .NET's solution for this usage issue.

Usage would go from:
format_page_range(0, 512)? -> HttpRange::new(0, 512)
and would also allow this to be used generally (ie. not just page ranges but also like blob download etc.)

This proposal adds a more general-case approach, in which we would need the following:

1. Generated HttpRange model with this impl. (or similar):

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct HttpRange {
    pub offset: u64,
    pub length: Option<u64>,
}

impl fmt::Display for HttpRange {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self.length {
            Some(length) => write!(f, "bytes={}-{}", self.offset, self.offset + length - 1),
            None => write!(f, "bytes={}-", self.offset),
        }
    }
}
impl From<HttpRange> for String { ... }
impl From<HttpRange> for HeaderValue { ... }

2. Generated code should take HttpRange instead of String

.tsp: Azure/azure-rest-api-specs#40095