Add request-side URL/body span attributes; split up RawTask._result

[o-nnerb]

Summary

• Adds url.scheme, server.address, server.port, url.path, and http.request.body.size to the request span RawTask starts, on top of the existing http.request.method/url.full. This mirrors what async-http-client's own built-in tracing gained in swift-server/async-http-client#906 (released in 1.36.1) — previously it only set http.request.method. url.query is deliberately left out since query strings can carry tokens/PII that shouldn't land on a span by default.
• Splits RawTask._result(environment:), which had grown into one ~210-line function doing hook notification, executor/network-path validation, client resolution, and the whole span lifecycle, into focused private methods (notifyDescriptorHooks, validateRequiredExecutor, waitForNetworkPath, resolveClient, runSession, executeTraced, startRequestSpan, setURLAttributes, endRequestSpan).

Why breaking-changes

No public API changed — this is an internal refactor plus additive span attributes. Labeled breaking-changes per explicit request rather than an assessment that anything actually breaks for consumers.

Design notes

• The refactor preserves task-local propagation timing exactly: the code this file exists for (owning the span lifecycle itself so ServiceContext.current survives, instead of delegating to async-http-client's tracing, which loses it on an EventLoop hop) is unaffected, since the extracted methods are still called synchronously within the same task — no new Task/EventLoop boundary was introduced.
• server.port falls back to the scheme's default (80/443) when the URL has none, mirroring async-http-client's DeconstructedURL/Scheme.defaultPort.

Test plan

• swift build — clean build
• swift test --filter "RequestServiceContextTests|SessionTests|RawTask" — 50/50 passing
• swift test --filter RequestDLTests — full suite, 1123/1123 passing

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.61%. Comparing base (600df4e) to head (e2d311b).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #331   +/-   ##
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  Coverage   98.61%   98.61%           
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  Files           5        5           
  Lines        1082     1082           
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  Hits         1067     1067           
  Misses         15       15           

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