feat: p4-compatible resource recharging ledger

[charmful0x]

metering rejection benchmark (p4 bundler case)

setup

• local HyperBEAM HTTP nodes.
• p4@1.0 + metering@1.0 + recharging-ledger@1.0 + bundler@1.0
• AO-provider case used trusted published recharger-ao-balance@1.0
• 25 rejected uploads per case (first attempt pass through, so expecting 24 402'd rejection)

results

default recharging-ledger only

avg   58.855 ms
p50   56.208 ms
min   51.857 ms
max   87.227 ms
402   25/25

recharging-ledger@1.0 + recharger-ao-balance@1.0 (external device package)

avg   598.738 ms
p50   591.374 ms
p95   644.382 ms
min   566.185 ms
max   677.337 ms
402   25/25

grace window

added recharging-ledger-grace as a small post-metering tolerance window -- this dont increase the user's visible/spendable balance. balance/3 still return the actual account balance, and p4 still uses that actual balance for preflight checks.

the grace only applies at charge/3: if the post-metering charge drifts slightly below zero, the ledger can accept it down to -Grace instead of rejecting after the work already ran

-> Default: 3600 units

todo

• metering rejection benchmark
• add charge-time grace window for small post-metering negative drift
• prepare hb config integration