chore(ntx-builder): selection and execution of sponsorship notes

[SantiagoPittella]

Summary

Part 2 of 3 for #2327

Transaction selection now works on note groups and each network note ("feature note") is selected together with the FEE_SPONSORSHIP notes bound to it, since a sponsorship may only be consumed in the same transaction as its feature note. Groups are packed atomically against the per-tx note budget and never split. When a feature note has more pending sponsorships than the cap (--max-sponsorships-per-note, and defaults to 3), a random subset is selected.

A new --require-sponsorship flag (default off) gates selection for zee-fees chains. With the flag off, behavior on zero-fee chains is unchanged

Since the consumability checker eliminates notes individually, the surviving ones are re-paired before execution and sponsorships whose feature note was eliminated are dropped. Failures of a sponsorship are attributed to its feature note, which carries the attempt tracking for the whole group.

Changelog

[[entry]]
scope       = "ntx-builder"
impact      = "added"
description = "Include fee sponsorship notes in network transactions alongside the note they sponsor, with a `--require-sponsorship` flag (default off) to skip unsponsored notes until their sponsorship arrives."