chore: drop redundant toReplayable overrides and derive Method token from enum name

[OmarAlJarrah]

Removes a small cluster of declarations in http/request that restate behavior they already inherit. All three changes are behavior-preserving.

Changes

RequestBody — drop the no-op toReplayable overrides on the replayable bodies

The base RequestBody.toReplayable() short-circuits to this whenever isReplayable() is true. The three private replayable bodies (BufferRequestBody, ByteArrayRequestBody, ResettableInputStreamRequestBody) all return true from isReplayable() and then re-declare an override that returns this — exactly what they'd inherit. The overrides are removed. (IoProvider stays imported; the base toReplayable still references it.)

FileRequestBody — drop the no-op override and its now-unused import

Same restatement, on the public body. The inherited toReplayable() still returns this — the same FileRequestBody — so transports that type-check is FileRequestBody for the zero-copy sendfile(2) path keep matching. With the override gone, import …io.IoProvider is unreferenced and is removed in the same change.

Method — derive the wire token from the enum name

Every constant passed a string literal identical to its own enum name (GET("GET", …), …), and toString() returned that string — which is what the default enum toString() already produces. The constructor parameter and the nine duplicated literals are dropped; the token is now a computed val method: String get() = name, and the default toString() stands. getMethod() remains public and callable, so request.method.method (okhttp adapter, Digest auth) and request.method.name (instrumentation) render the same token as before.

API

Two explicit overrides become inherited/default, so their lines drop from sdk-core/api/sdk-core.api (regenerated and committed):

• FileRequestBody.toReplayable (…IoProvider;)…
• Method.toString ()Ljava/lang/String;

getMethod() is unchanged. The Method enum constructor is implicitly private and not in the snapshot, so dropping its parameter is not itself an API change.

Verification

• :sdk-core:compileKotlin, ktlint, and apiCheck (against the regenerated snapshot) pass.
• Method, RequestBody, and FileRequestBody test suites pass — including MethodTest's toString()-equals-token check, which holds under the default enum toString().

Closes #174