feat(redis_interface): instrument Redis commands with external service call event emission

[spritianeja03]

Type of Change

• Bugfix
• New feature
• Enhancement
• Refactoring
• Dependency updates
• Documentation
• CI/CD

Description

This PR instruments every Redis command in both the fred and redis_rs backends with per-call ExternalServiceCall event emission, making Redis latency and errors visible through the same observability pipeline used for key-manager calls.

Key Changes

1. crates/redis_interface/src/observability.rs (new)

   • observe() async helper wraps each Redis command future, records wall-clock latency, and emits an ExternalServiceCall event (service_name: "redis", endpoint: <command name>)
   • is_enabled() fast-path guard: when the emitter is a no-op (emission disabled), the request-ID lookup and event construction are skipped entirely — Redis is the hottest call path and the guard keeps overhead near zero
   • No event is emitted when REQUEST_ID is absent (background workers, drainer, scheduler) since there is no API request to correlate to

2. crates/router_env/src/request_context.rs (new)

   • REQUEST_ID tokio task-local propagates the current request ID from the actix RequestIdentifier middleware into deeply nested async code without threading it through every call site
   • try_get() returns None outside a request scope (background work), which the observe() helper treats as "no emission needed"

3. Both command modules updated (crates/redis_interface/src/module/fred/commands.rs, crates/redis_interface/src/module/redis_rs/commands.rs)

   • Every public async command method now wraps its body with the observed!() macro (sugar for observe(self, "CMD", { body }).await)

Additional Changes

• This PR modifies the API contract
• This PR modifies the database schema
• This PR modifies application configuration/environment variables

Motivation and Context

Redis is called on virtually every payment and storage operation, yet its latency contribution is invisible — it appears as undifferentiated time in request spans. This PR makes each Redis command emit a discrete event carrying the command name, latency, success status, and request ID. Events flow through the same ExternalServiceCall Kafka topic introduced for key-manager instrumentation, and land in ClickHouse where per-command latency histograms, error rates, and per-merchant Redis usage patterns can be queried.

How did you test it?

• Ran cargo test -p redis_interface — all existing tests pass
• Verified the is_enabled() fast-path guard prevents any allocation when emission is disabled (no-op emitter returns false without acquiring the task-local)

Checklist

• I formatted the code cargo +nightly fmt --all
• I addressed lints thrown by cargo clippy
• I reviewed the submitted code
• I added unit tests for my changes where possible

Closes #13090

[semanticdiff-com]

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Changed Files

File	Status
crates/router_env/src/request_id.rs	92% smaller
crates/drainer/src/connection.rs	89% smaller
crates/storage_impl/src/mock_db.rs	89% smaller
crates/redis_interface/src/test.rs	89% smaller
crates/storage_impl/src/redis.rs	77% smaller
crates/storage_impl/src/lib.rs	69% smaller
crates/redis_interface/src/module/fred/commands.rs	65% smaller
crates/storage_impl/src/connection.rs	63% smaller
crates/router/src/routes/app.rs	53% smaller
crates/redis_interface/src/lib.rs	50% smaller
crates/router/src/connection.rs	39% smaller
crates/redis_interface/src/module/redis_rs/commands.rs	29% smaller
crates/storage_impl/src/redis/pub_sub.rs	19% smaller
crates/redis_interface/src/metrics.rs	11% smaller
crates/redis_interface/src/module/fred.rs	7% smaller
crates/redis_interface/src/module/redis_rs.rs	7% smaller
Cargo.lock	Unsupported file format
crates/common_utils/src/external_service.rs	0% smaller
crates/redis_interface/Cargo.toml	Unsupported file format
crates/redis_interface/src/types.rs	0% smaller
crates/router/src/services.rs	0% smaller
crates/router_env/src/lib.rs	0% smaller
crates/router_env/src/request_context.rs	0% smaller