Land #794: entry-point cost budgets, admin multisig decision, mainnet checklist

[godamongstmen897]

Merges contributor PR #794 (mathstickz) onto main with these fixes:

• Compile errors in cost_tests:
  • The crate is no_std, so println! needs extern crate std.
  • InvocationResources::instructions is i64, and there is no memory_read_bytes (mem_bytes is the memory figure).
  • Disputes now need a delivered milestone (Disputes have no timeout; an absent arbiter locks the milestone's funds indefinitely #784), so the dispute flows mark delivery first.
• Add resource-cost budget tests for the main entry points and track regressions #764 acceptance: the test only asserted instructions > 0, so it couldn't catch a regression. It now enforces per-entry-point budgets from the current baselines: exact for ledger write entries, about 10% headroom for instructions and write bytes. I checked it by adding an extra persistent write to fund, which fails with fund: 5 ledger writes exceeds the budget of 4.

Current numbers (gzip-free host metering):

flow	instructions	write entries	write bytes
initialize	204,879	6	1,508
fund	292,583	4	1,196
mark_delivered	151,720	3	448
approve_milestone	385,176	7	1,168
claim_auto_release	397,882	6	1,056
raise_dispute	216,611	5	636
resolve_dispute	432,287	7	1,056

#762 is covered by ADMIN_MULTISIG_DECISION.md, and #763 by MAINNET.md, linked from the README.

Local run: all checks pass with 1234 tests.

Closes #762, closes #763, closes #764

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