fix: avoid setting db.cleans to nil on Close (ethereum#29309)

[hmlee-wm]

Summary

Remove the db.cleans = nil assignment in Close() to prevent a potential data race with concurrent node() or commit() calls that access db.cleans without a lock.

Upstream References

PR	Description
#29309	triedb/hashdb: Avoid setting db.cleans on Close

Problem

db.cleans is accessed without a lock in node() (L189, L214) and commit() (L532), while Close() sets it to nil also without a lock. A concurrent goroutine that passes the db.cleans != nil check and then calls db.cleans.Get/Set after Close() nullifies the pointer will panic.

Changes

• triedb/hashdb/database.go: Remove db.cleans = nil in Close().
• db.cleans.Reset() already clears the cache contents; the cleans field is collected by GC along with its owner db, so the nil assignment serves no purpose.
• No behavior change for normal operation.

[eomti-wm]

LGTM

[colinkim]

LGTM