deno: `init()` never registers the channel-injection hooks, though Deno supports them

[isaacs]

Deno 2.9.2 has a working Module.registerHooks, and hasStableSyncModuleHooks already returns true for Deno unconditionally (register.ts:20). Calling the register function directly works:

$ deno run -A reg.mjs
marker after register: {"runtime":[]}    # hooks registered

But @sentry/deno's init() never calls it:

$ deno run -A nospans.mjs
orchestrion marker: undefined

Node's init() calls registerDiagnosticsChannelInjection() and then detectOrchestrionSetup(). Deno instead expects the user to remember deno run --import=@sentry/deno/import app.ts, and gives no warning at all if they forget. All 22 channel integrations still install and report Integration installed.

Work item. Call registerDiagnosticsChannelInjection() from @sentry/deno's init() behind the same enableRuntimeChannelInjection option Node uses, and call detectOrchestrionSetup() after client creation. Keep @sentry/deno/import working for the case where modules are imported before init().

**Prior art **(related history only). #21451 (merged) added the @sentry/deno/import runtime hook, and #22790 (merged) raised the floor to Deno >= 2.8.3, which is what makes the Module.registerHooks path safe to call unconditionally. No issue covers calling it from init().

[linear-code]

JS-3518