fix: add more recent zero point for wallet birthday (see issue #4176) (…

…#4275)

Description
--- 
Add logic to tackle issue #4176, which aims at improving birthday representation for Cipher Seed generation.

Motivation and Context
--- 
The goal of this PR is to resolve issue #4176.  The current version is supposed to allow a more recent genesis for wallet birthdays (it actually depends on the genesis block of the Tari network, we wish to work with). Moreover, it updates the version. Moreover, if the birthday does not fit within the `u16` type range, we update to a new version. 

How Has This Been Tested?
--- 
Add simple tests to check if logic is correct.

base_layer/key_manager/src/cipher_seed.rs

@@ -23,7 +23,8 @@
 use std::{
     convert::TryFrom,
     mem::size_of,
-    time::{SystemTime, UNIX_EPOCH},
+    ops::Add,
+    time::{Duration, SystemTime, UNIX_EPOCH},
 };
 
 use argon2::{
@@ -54,6 +55,8 @@ use crate::{
 };
 
 const CIPHER_SEED_VERSION: u8 = 0u8;
+// seconds elapsed from unix epoch until '2022-01-01' == 60 * 60 * 24 * 365 * 52
+pub const BIRTHDAY_GENESIS_FROM_UNIX_EPOCH: u64 = 1639872000;
 pub const DEFAULT_CIPHER_SEED_PASSPHRASE: &str = "TARI_CIPHER_SEED";
 const ARGON2_SALT_BYTES: usize = 16;
 pub const CIPHER_SEED_BIRTHDAY_BYTES: usize = 2;
@@ -119,7 +122,12 @@ impl CipherSeed {
     #[cfg(not(target_arch = "wasm32"))]
     pub fn new() -> Self {
         const SECONDS_PER_DAY: u64 = 24 * 60 * 60;
-        let days = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs() / SECONDS_PER_DAY;
+        let birthday_genesis_date = UNIX_EPOCH.add(Duration::from_secs(BIRTHDAY_GENESIS_FROM_UNIX_EPOCH));
+        let days = SystemTime::now()
+            .duration_since(birthday_genesis_date)
+            .unwrap()
+            .as_secs() /
+            SECONDS_PER_DAY;
         let birthday = u16::try_from(days).unwrap_or(0u16);
         CipherSeed::new_with_birthday(birthday)
     }