fix: improve MessageV0.getAccountKeys API ergonomics

[jstarry]

Problem

The ergonomics of MessageV0.getAcccountKeys isn't great when writing code that can handle legacy or v0 messages:

const accountKeysFromLookups = txWithMeta.meta?.loadedAddresses;
const accountKeys = message.getAccountKeys(accountKeysFromLookups && {
  accountKeysFromLookups,
});

Summary of Changes

Allow args in GetAccountKeysArgs to be undefined or null for improved ergonomics:

const accountKeys = message.getAccountKeys({
  accountKeysFromLookups: txWithMeta.meta?.loadedAddresses,
});

Fixes #

[codecov]

Codecov Report

Merging #28042 (4ff5186) into master (e6687b8) will increase coverage by 0.3%.
The diff coverage is 97.0%.

@@            Coverage Diff            @@
##           master   #28042     +/-   ##
=========================================
+ Coverage    77.3%    77.6%   +0.3%     
=========================================
  Files          55       55             
  Lines        2889     2918     +29     
  Branches      402      406      +4     
=========================================
+ Hits         2234     2267     +33     
+ Misses        514      510      -4     
  Partials      141      141