Simplify Bolt11 Payments and Remove Redundant Code

[shaavan]

resolves #3262
builds on: #3342

Summary

This PR introduces pay_for_bolt11_invoice, simplifying how Bolt11 payments are processed by allowing direct invoice-based payments while still enabling custom routing parameters. With this change, the redundant bolt11_payment.rs utility functions are no longer needed and have been removed.

Why This Change?

• Previously, paying a Bolt11 invoice required manually extracting payment_id, payment_hash, and other parameters before passing them to send_payment.
• pay_for_bolt11_invoice introduces a more streamlined approach, mirroring the existing convenience of Bolt12 payments.
• With this function now handling parameter extraction within ChannelManager, bolt11_payment.rs is redundant and can be safely removed.

Changes

• Introduced pay_for_bolt11_invoice:
  • Takes a Bolt11 invoice directly.
  • Allows users to set custom routing parameters via RouteParametersConfig.
• Removed bolt11_payment.rs:
  • All relevant logic is now handled within ChannelManager.
  • Removed associated test cases for redundant utility functions.

Impact

• Reduces complexity for Bolt11 payments.
• Cleans up redundant code, making the implementation more maintainable.

[TheBlueMatt]

Thanks! This needs rebase now.

[shaavan]

Updated from pr3617.01 to pr3617.02 (diff):

Changes:

1. Rebase on main.

[shaavan]

Updated from pr3617.02 to pr3617.03 (diff):
Addressed @TheBlueMatt comments

Changes:

1. Introduce payment_id as parameter, and update documentation

[codecov]

Codecov Report

Attention: Patch coverage is 84.50704% with 11 lines in your changes missing coverage. Please review.

Project coverage is 88.57%. Comparing base (1610854) to head (16368c0).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/outbound_payment.rs	81.57%	3 Missing and 4 partials ⚠️
lightning/src/events/mod.rs	0.00%	2 Missing ⚠️
lightning/src/routing/router.rs	86.66%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3617      +/-   ##
==========================================
- Coverage   88.60%   88.57%   -0.03%     
==========================================
  Files         151      150       -1     
  Lines      118454   118377      -77     
  Branches   118454   118377      -77     
==========================================
- Hits       104957   104856     -101     
- Misses      10985    10990       +5     
- Partials     2512     2531      +19     

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[TheBlueMatt]

thanks!