Perf/dlmalloc guest allocator

[jotabulacios]

The guest allocator moves from embedded-alloc's TLSF heap to dlmalloc, with TLSF kept one
flag away (tlsf-alloc) for fallback. dlmalloc sits on a bump provider that hands it
page-aligned chunks of the guest heap, so it still reuses freed memory — no OOM — while
each alloc and free costs fewer guest instructions than TLSF.

Isolated A/B on the same tree, only the feature differs: guest cycles drop 11.2% on a
10-transfer ethrex block (1,702,365 → 1,511,225) and 13.1% on a 20-transfer one
(3,915,738 → 3,404,649). In the guest profile the allocator goes from 24.4% of cycles to
9.5%.

[diegokingston]

/bench

[github-actions]

Benchmark — real block (ethrex_mainnet_25368371.bin) (median of 3)

_{continuations · epoch 2^22 · 12 epochs}

Metric	main	PR	Δ
Peak heap	51856 MB	53205 MB	+1349 MB (+2.6%) ⚪
Prove time	159.217s	155.437s	-3.780s (-2.4%) ⚪

✅ No significant change.

_{Prove-time spread 3.0% (155.437s / 153.306s / 157.933s)}

_{Commit: 590c340 · Baseline: cached · Runner: self-hosted bench}

[diegokingston]

/bench

[MauroToscano]

/bench