fix: leave balance for earned leaves in backdated Leave Application dashboard

[ruchamahabal]

Problem

1. Create Leave Policy Assignment for earned leaves with 8 leaves allocated at first.

   

2. Earned Leaves are allocated in April and May end.

3. Try creating a backdated leave application for April. It shows balance as 12 and 4 leaves expired. Although 12 leaves weren't available on April 1st, only 8 were available and there were no expired leaves

This problem only occurs in the case of Earned Leaves because they are added based on policy frequency, unlike other leaves which are allocated all at once on allocation creation.

The leave balance and leave balance summary reports, and balance in the leave application all work fine. The issue is only with the leave application dashboard.

Fix

Don't consider the entire allocation, only consider the ledger entries that fall within that period.

[codecov]

Codecov Report

Merging #31253 (719fa43) into develop (c57125a) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head 719fa43 differs from pull request most recent head ef9c34e. Consider uploading reports for the commit ef9c34e to get more accurate results

@@             Coverage Diff             @@
##           develop   #31253      +/-   ##
===========================================
- Coverage    63.49%   63.43%   -0.06%     
===========================================
  Files          986      986              
  Lines        67440    67439       -1     
===========================================
- Hits         42819    42781      -38     
- Misses       24621    24658      +37     

Impacted Files	Coverage Δ
.../hr/doctype/leave_application/leave_application.py	82.34% <100.00%> (-0.04%)	⬇️
...tch_item_expiry_status/batch_item_expiry_status.py	67.92% <0.00%> (-24.53%)	⬇️
...wise_balance_history/batch_wise_balance_history.py	67.79% <0.00%> (-22.04%)	⬇️
...rpnext/accounts/doctype/shareholder/shareholder.py	80.00% <0.00%> (-10.00%)	⬇️
...e_sales_analytics/supplier_wise_sales_analytics.py	81.96% <0.00%> (-8.20%)	⬇️
...urity_shortfall/process_loan_security_shortfall.py	93.75% <0.00%> (-6.25%)	⬇️
erpnext/hr/doctype/job_offer/job_offer.py	82.92% <0.00%> (-4.88%)	⬇️
...pnext/setup/doctype/sales_partner/sales_partner.py	65.21% <0.00%> (-4.35%)	⬇️
...e/asset_value_adjustment/asset_value_adjustment.py	86.04% <0.00%> (-3.49%)	⬇️
erpnext/stock/doctype/warehouse/warehouse.py	79.02% <0.00%> (-2.10%)	⬇️
... and 10 more

[ruchamahabal]

Unrelated test failure