impl(storage): explicitly cast span data to supported common::AttributeValue type

[scotthart]

std::size_t on some platforms didn't always translate to a type contained in Otel's AttributeValue type:

using AttributeValue =
    nostd::variant<bool,
                   int32_t,
                   int64_t,
                   uint32_t,
                   double,
                   const char *,
                   nostd::string_view,
                   nostd::span<const bool>,
                   nostd::span<const int32_t>,
                   nostd::span<const int64_t>,
                   nostd::span<const uint32_t>,
                   nostd::span<const double>,
                   nostd::span<const nostd::string_view>,
                   // Not currently supported by the specification, but reserved for future use.
                   // Added to provide support for all primitive C++ types.
                   uint64_t,
                   // Not currently supported by the specification, but reserved for future use.
                   // Added to provide support for all primitive C++ types.
                   nostd::span<const uint64_t>,
                   // Not currently supported by the specification, but reserved for future use.
                   // See https://github.com/open-telemetry/opentelemetry-specification/issues/780
                   nostd::span<const uint8_t>>;

---

This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.92%. Comparing base (8bada09) to head (d6819af).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15119   +/-   ##
=======================================
  Coverage   92.92%   92.92%           
=======================================
  Files        2389     2389           
  Lines      214852   214852           
=======================================
+ Hits       199641   199656   +15     
+ Misses      15211    15196   -15     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.