fix: bom valuation - handle lack of LPP

[ankush]

• Handle a case where BOM uses LPP for valuation but RM doesn't have it.
• Add a basic test for LPP.

[codecov]

Codecov Report

Merging #30454 (7f920d5) into develop (69ae266) will increase coverage by 8.55%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop   #30454      +/-   ##
===========================================
+ Coverage    52.21%   60.76%   +8.55%     
===========================================
  Files         1082     1082              
  Lines        68691    68691              
===========================================
+ Hits         35866    41741    +5875     
+ Misses       32825    26950    -5875     

Impacted Files	Coverage Δ
erpnext/manufacturing/doctype/bom/bom.py	87.59% <100.00%> (+0.15%)	⬆️
...unts/report/purchase_register/purchase_register.py	32.19% <0.00%> (-41.10%)	⬇️
...ext/accounts/report/balance_sheet/balance_sheet.py	36.36% <0.00%> (-21.82%)	⬇️
...e_purchase_register/item_wise_purchase_register.py	58.00% <0.00%> (-17.00%)	⬇️
...t/accounts/report/sales_register/sales_register.py	71.51% <0.00%> (-1.82%)	⬇️
...t/accounts/report/general_ledger/general_ledger.py	67.57% <0.00%> (-1.71%)	⬇️
...cial_statement/consolidated_financial_statement.py	89.06% <0.00%> (-1.57%)	⬇️
.../report/accounts_receivable/accounts_receivable.py	70.94% <0.00%> (-0.86%)	⬇️
...ype/account/chart_of_accounts/chart_of_accounts.py	77.39% <0.00%> (-0.69%)	⬇️
...next/accounts/doctype/subscription/subscription.py	82.14% <0.00%> (-0.55%)	⬇️
... and 220 more