chore(deps): replace golang.org/x/crypto/sha3 with go-keccak, upgrade x/crypto

[rvagg]

Replace all usage of golang.org/x/crypto/sha3.NewLegacyKeccak256() with github.com/filecoin-project/go-keccak, which vendors the assembly-optimised Keccak permutation from x/crypto@v0.43.0. Starting with x/crypto v0.44.0, the upstream package removed its amd64 assembly in favor of Go's standard library crypto/sha3, which does not provide an assembly fast path for legacy Keccak functions.

With the keccak dependency decoupled, upgrade golang.org/x/crypto to v0.47.0.

Ref: #1055
Ref: filecoin-project/lotus#13443
Ref: ethereum/go-ethereum#33323

[Copilot]

Pull request overview

Updates the project’s legacy Keccak-256 hashing implementation to preserve an amd64 assembly fast path while allowing golang.org/x/crypto to be upgraded independently.

Changes:

• Replaced golang.org/x/crypto/sha3.NewLegacyKeccak256() usage with github.com/filecoin-project/go-keccak.NewLegacyKeccak256().
• Upgraded golang.org/x/crypto to v0.47.0 (and related indirect golang.org/x/* module versions).
• Added github.com/filecoin-project/go-keccak v0.1.0 to module dependencies.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
merkle/merkle.go	Switches legacy Keccak hasher construction to go-keccak while keeping the same call sites.
go.mod	Adds go-keccak and upgrades golang.org/x/crypto (plus indirect golang.org/x/* updates).
go.sum	Records checksum entries for go-keccak and updated golang.org/x/* module versions.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.57%. Comparing base (dc95659) to head (293f335).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1064      +/-   ##
==========================================
+ Coverage   65.39%   65.57%   +0.18%     
==========================================
  Files          81       81              
  Lines        8001     8001              
==========================================
+ Hits         5232     5247      +15     
+ Misses       2236     2226      -10     
+ Partials      533      528       -5     

Files with missing lines	Coverage Δ
merkle/merkle.go	91.91% <100.00%> (ø)

... and 6 files with indirect coverage changes

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