feat: subscription refactor

[hrwX]

• Reopened the PR refactor: subscriptions #29870 here as the branch was messed up.
• Reduced complexity associated with invoice generation function, got rid of is_postpaid_to_invoice and is_prepaid_to_invoice.

def can_generate_new_invoice(self) -> bool:
    if self.cancelation_date:
	    return False
    elif self.generate_invoice_at_period_start and (
	    getdate(frappe.flags.current_date) == getdate(self.current_invoice_start)
	    or self.is_new_subscription()
    ):
	    return True
    elif getdate(frappe.flags.current_date) == getdate(self.current_invoice_end):
	    if self.has_outstanding_invoice() and not self.generate_new_invoices_past_due_date:
		    return False
    
	    return True
    else:
	    return False

• The invoices won't be generated randomly, they will only be generated either at the beginning of the period or the end of the period depending on the configuration, eliminating the randomness of earlier implementation.
• Removed redundant child table for saving invoices. Added a link field in Sales and Purchase Invoice
• New Subscription Layout
  

no-docs

[stale]

This pull request has been automatically marked as inactive because it has not had recent activity. It will be closed within 3 days if no further activity occurs, but it only takes a comment to keep a contribution alive :) Also, even if it is closed, you can always reopen the PR when you're ready. Thank you for contributing.

[federicocalvo]

Hi, this is the most important doctype/function for any service company. And it is becoming more and more common, so not only does a refactor make sense, but it already marks a horizon with improvements.

[stale]

This pull request has been automatically marked as inactive because it has not had recent activity. It will be closed within 3 days if no further activity occurs, but it only takes a comment to keep a contribution alive :) Also, even if it is closed, you can always reopen the PR when you're ready. Thank you for contributing.

[codecov]

Codecov Report

Merging #30963 (fbbf6e2) into develop (8c410c6) will increase coverage by 0.48%.
Report is 192 commits behind head on develop.
The diff coverage is 84.27%.

❗ Current head fbbf6e2 differs from pull request most recent head 380aede. Consider uploading reports for the commit 380aede to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #30963      +/-   ##
===========================================
+ Coverage    64.11%   64.59%   +0.48%     
===========================================
  Files          785      788       +3     
  Lines        60780    61371     +591     
===========================================
+ Hits         38970    39645     +675     
+ Misses       21810    21726      -84     

Files Changed	Coverage Δ
...t/crm/doctype/twitter_settings/twitter_settings.py	0.00% <0.00%> (ø)
...next/accounts/doctype/subscription/subscription.py	84.69% <88.74%> (+1.99%)	⬆️

... and 50 files with indirect coverage changes