[wip] another btree

[AskAlexSharov]

for: #17988

 ┌─────────────────────────┬────────────────┬──────────────────┬─────────────────────────────┐
  │        Operation        │   anacrolix    │     tidwall      │              Δ              │
  ├─────────────────────────┼────────────────┼──────────────────┼─────────────────────────────┤
  │ Set 100k keys           │ 23 ms, 10.8 MB │ 26.7 ms, 15.6 MB │ 14% faster, 31% less memory │
  ├─────────────────────────┼────────────────┼──────────────────┼─────────────────────────────┤
  │ Set 10k keys            │ 1.5 ms, 1.1 MB │ 1.8 ms, 1.7 MB   │ 14% faster, 35% less memory │
  ├─────────────────────────┼────────────────┼──────────────────┼─────────────────────────────┤
  │ Get (random, 100k map)  │ 203 ns         │ 210 ns           │ ~3% faster                  │
  ├─────────────────────────┼────────────────┼──────────────────┼─────────────────────────────┤
  │ SetGet (mixed, 10k map) │ 211 ns         │ 221 ns           │ ~5% faster                  │
  └─────────────────────────┴────────────────┴──────────────────┴─────────────────────────────┘

see also:
anacrolix/btree#1
anacrolix/btree#3

[Copilot]

Pull request overview

Switches the in-memory ordered map used for StorageDomain buffering from tidwall/btree to anacrolix/btree, aligning with the performance/memory investigation in #17988 and keeping prefix-iteration support intact in the state aggregator pipeline.

Changes:

• Promote github.com/anacrolix/btree v0.1.1 to a direct dependency in go.mod.
• Replace tidwall/btree map usage in TemporalMemBatch with anacrolix/btree (MakeMap, Upsert, Iterator, Reset).
• Adapt the storage-domain prefix-iteration path (debugIteratePrefixLatest) to consume an *anacrolix/btree.Map and its iterator API.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
go.mod	Makes github.com/anacrolix/btree a direct requirement (was indirect).
db/state/temporal_mem_batch.go	Migrates the StorageDomain in-RAM structure to anacrolix/btree and updates write/clear/merge logic accordingly.
db/state/domain_stream.go	Updates the RAM portion of the multi-source prefix iterator to use anacrolix/btree iterators.

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[yperbasis]

Submodule execution-spec-tests should not change

addressed

[anacrolix]

I'll bow out of pushing this one for now.