feat: add nowInBigIntNanoSeconds to utils (#756)

# Motivation

We actually use `nowInBigIntNanoSeconds` everywhere so let's add it to
utils.

# Changes

- Copy function `nowInBigIntNanoSeconds` to `@dfinity/utils`.

---------

Signed-off-by: David Dal Busco <david.dalbusco@dfinity.org>
Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 - Added `memoToNeuronSubaccount` and `memoToNeuronAccountIdentifier`.
 - Support new neuron field `voting_power_refreshed_timestamp_seconds`.
+- Add `nowInBigIntNanoSeconds` to `@dfinity/utils`, a trivial function that is actually used across all our dapps.
 
 ## Build
 

packages/utils/README.md

@@ -55,6 +55,7 @@ npm i @dfinity/agent @dfinity/candid @dfinity/principal
 - [decodeBase32](#gear-decodebase32)
 - [bigEndianCrc32](#gear-bigendiancrc32)
 - [secondsToDuration](#gear-secondstoduration)
+- [nowInBigIntNanoSeconds](#gear-nowinbigintnanoseconds)
 - [debounce](#gear-debounce)
 - [toNullable](#gear-tonullable)
 - [fromNullable](#gear-fromnullable)
@@ -302,6 +303,16 @@ Parameters:
 
 [:link: Source](https://github.com/dfinity/ic-js/tree/main/packages/utils/src/utils/date.utils.ts#L43)
 
+#### :gear: nowInBigIntNanoSeconds
+
+Returns the current timestamp in nanoseconds as a `bigint`.
+
+| Function                 | Type           |
+| ------------------------ | -------------- |
+| `nowInBigIntNanoSeconds` | `() => bigint` |
+
+[:link: Source](https://github.com/dfinity/ic-js/tree/main/packages/utils/src/utils/date.utils.ts#L115)
+
 #### :gear: debounce
 
 | Function   | Type                                                                              |