chore: simplify http/response memoization, docs, and exception constructors

[OmarAlJarrah]

Summary

Three small, self-contained cleanups in the http/response subsystem. None changes runtime behavior — each reuses a stdlib primitive, fixes stale documentation, or removes copy-pasted boilerplate.

1. ParsedResponse — memoize with kotlin.Result

The class hand-rolled a private Outcome sealed class (Success/Failure) purely to memoize the handler's result-or-throw. That is exactly what kotlin.Result models, and the module already uses runCatching/getOrThrow elsewhere. Storing the memo as a nullable Result<T>? keeps the deliberate "null success vs. not-yet-parsed" distinction, and runCatching catches Throwable (not just Exception), so the existing semantics — including memoizing an Error so a later call can't re-read the single-use body — are preserved exactly. Call sites are unchanged.

2. ResponseBody — align the class KDoc with the real contract

The class KDoc described a byteStream/bytes/string API that this type never declared; its only read accessor is source(): BufferedSource. The doc was also the sole reference to java.io.InputStream, so it dragged along an unused import (which ktlint's no-unused-imports rule under allWarningsAsErrors would flag once the doc stopped mentioning it). The KDoc now describes the actual source() contract and the import is removed.

3. HttpException — funnel the 18 subclass constructors through one base constructor

Each of the 18 concrete subclasses repeated the same six-argument block unpacking response.status/response.headers/response.body into the base constructor. Hoisting that into a single protected constructor that takes the Response directly collapses every subclass to a one-line delegation. The subclasses' public (response, message?, cause?, value?) surfaces are byte-for-byte unchanged.

API impact

Adds one protected constructor to HttpException; the regenerated sdk-core.api snapshot is committed. No public signatures change.

Verification

./gradlew :sdk-core:build passes — tests, ktlint, detekt, apiCheck, and the coverage gate.

Closes #175