Add high-level HTTP method helpers to zigttp:fetch

[srdjan]

Motivation

• Improve handler ergonomics by exposing high-level HTTP method helpers so Zig-specific request boilerplate is not required in zigts handlers.
• Keep virtual-module contracts, egress-host extraction, and runtime delegation intact so verification and policy tooling continue to work.

Description

• Added get, post, put, patch, and delete exports to zigttp:fetch with the same effect/contract_extractions metadata as fetch so proof and egress extraction remain correct (file: packages/modules/src/net/fetch.zig).
• Implemented fetchWithMethod which validates args, forces the HTTP method, and delegates to the existing runtime callback path (state.call_fn) so runtime behavior is unchanged.
• Implemented cloneWithMethod which copies an init object via sdk.objectKeys/sdk.objectGet and sets the method field, preserving other RequestInit fields for the helpers.
• Updated documentation to advertise the new helpers and describe that they clone init and set method automatically (file: docs/virtual-modules/net/fetch.md).

Testing

• Attempted to run formatting and the Zig test suite with zig fmt packages/modules/src/net/fetch.zig and zig build test-zigts, but the environment lacks Zig so both commands failed with zig: command not found and automated tests could not be executed.
• No new Zig test blocks were added in this change; the change is limited to packages/modules/src/net/fetch.zig and the corresponding docs update.

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Codex Task