fix(tee-prover): fix deserialization of duration in envy config

Relevant logs from the `stage` environment showcasing the issue:
https://grafana.matterlabs.dev/goto/IC-9k4eIR?orgId=1

Error message from the above logs:
```
Error: missing value for field initial_retry_backoff
```

The root cause of the problem supposedly boils down to the mismatch
between the expected format of `TEE_PROVER_INITIAL_RETRY_BACKOFF` and
the actual format. We export it as follows:
```
export TEE_PROVER_INITIAL_RETRY_BACKOFF=1
```
which is not supported as explained here:
serde-rs/serde#339 (comment)

core/bin/zksync_tee_prover/Cargo.toml

@@ -18,6 +18,7 @@ envy.workspace = true
 reqwest.workspace = true
 secp256k1 = { workspace = true, features = ["serde"] }
 serde = { workspace = true, features = ["derive"] }
+serde_with.workspace = true
 thiserror.workspace = true
 tokio = { workspace = true, features = ["full"] }
 tracing.workspace = true

core/bin/zksync_tee_prover/src/config.rs

@@ -2,11 +2,13 @@ use std::{path::PathBuf, time::Duration};
 
 use secp256k1::SecretKey;
 use serde::Deserialize;
+use serde_with::{serde_as, DurationSecondsWithFrac};
 use url::Url;
 use zksync_env_config::FromEnv;
 use zksync_types::tee_types::TeeType;
 
 /// Configuration for the TEE prover.
+#[serde_with::serde_as]
 #[derive(Debug, Clone, Deserialize)]
 pub(crate) struct TeeProverConfig {
     /// The private key used to sign the proofs.
@@ -22,10 +24,12 @@ pub(crate) struct TeeProverConfig {
     pub max_retries: usize,
     /// Initial back-off interval when retrying recovery on a retriable error. Each subsequent retry interval
     /// will be multiplied by [`Self.retry_backoff_multiplier`].
+    #[serde_as(as = "DurationSecondsWithFrac")]
     pub initial_retry_backoff: Duration,
     /// Multiplier for the back-off interval when retrying recovery on a retriable error.
     pub retry_backoff_multiplier: f32,
     /// Maximum back-off interval when retrying recovery on a retriable error.
+    #[serde_as(as = "DurationSecondsWithFrac")]
     pub max_backoff: Duration,
 }