Add --disable-output-confirmations flag

[utxo-detective]

Summary

Add a `--disable-output-confirmations` flag (and `ORD_DISABLE_OUTPUT_CONFIRMATIONS` env var) that switches the `/output` endpoint to a faster code path by skipping the confirmations lookup.

Problem

The `/output` endpoint currently makes up to 2 sequential Bitcoin Core RPC calls for every spent output:

1. `gettxout(txid, vout, true)` — returns `None` for spent outputs
2. `getrawtransaction(txid, true)` — verbose mode to get `confirmations`

The verbose `getrawtransaction` is more expensive than non-verbose because bitcoind must look up the block, compute confirmations from current chain height, and serialize a full decoded JSON response with all vins/vouts (~3.5x larger response).

Prior to the confirmations feature, the endpoint used a single non-verbose `getrawtransaction` (returns raw hex, deserialized client-side) plus a simple `gettxout` spent check.

Benchmarks

Tested against a local Bitcoin Core node (fully synced, block 940219) with 200 concurrent requests using 200 unique transactions:

Individual RPC call latency at 200 concurrent:

RPC Call	p50	p99
`getrawtransaction` (non-verbose)	21ms	60ms
`getrawtransaction` (verbose)	27ms	75ms
`gettxout`	26ms	74ms

Full /output endpoint simulation at 200 concurrent:

Path	Total	p50	p99
Fast (non-verbose getrawtx + gettxout)	497ms	71ms	158ms
Current (gettxout + verbose getrawtx)	533ms	86ms	189ms

The fast path shows ~20% lower p50 and p99 latency at high concurrency. The improvement compounds in production where ord is also contending with index write locks and other concurrent operations.

Response size comparison for a typical transaction:

• Non-verbose `getrawtransaction`: ~419 bytes
• Verbose `getrawtransaction`: ~1,464 bytes (3.5x larger)

Solution

When `--disable-output-confirmations` is set, `get_output_info` uses the pre-confirmations code path:

• Single non-verbose `getrawtransaction` call
• Simple `is_output_spent` check via `gettxout`
• `confirmations` field returns `0`

Default behavior is unchanged. This is an opt-in optimization for operators who prioritize API throughput over confirmations data.

Test plan

• `/output` returns correct data with flag enabled (all fields except confirmations)
• `/output` returns confirmations when flag is not set (default unchanged)
• Flag works via CLI (`--disable-output-confirmations`) and env var (`ORD_DISABLE_OUTPUT_CONFIRMATIONS=1`)