#36282 Update leveldb subtree to latest master

• Stop LevelDB headers from generating unused constant compiler warnings
• Unblocks enabling stricter unused constant variable checks across the project

Updates the `src/leveldb` subtree to latest master, importing bitcoin-core/leveldb-subtree#65. The change replaces `static const` with `inline constexpr` in LevelDB headers to prevent unused constant variable warnings when headers are included.

Problem: Unused `static const` variables in LevelDB headers trigger compiler warnings, blocking the enablement of `-Wunused-const-variable` in the main build (#36275).

P3 · unblocks #36275

• P3 because it unblocks enabling stricter compiler warning flags across the build
• Eliminates header warnings in vendored storage dependency code

Worthwhile subtree update that carries an internal header refactor. The description notes it is 'Used in #36275', where enabling `-Wunused-const-variable` relies on eliminating unused const warnings from LevelDB headers.

Membership: LevelDB is a vendored subtree tracked under utils.

Factors: security/stability 0, bug 0, performance 0, user value 0, leverage 1

• Ready for review as a clean and minimal subtree update

The PR is a clean, minimal subtree update (+16/-16) with green CI and no blockers.

Author status: active

• Smooth consensus on importing the upstream changes
• Code review approval without objections (l0rinc)

Positive; straightforward subtree sync approved by l0rinc.

The subtree sync was reviewed and ACKed promptly with no objections.

• l0rinc left a code review ACK on 7528f79

Review verdicts (DrahtBot): 1

• ACK: l0rinc

Enables:

• #36275

0 lines under test/bench/ci.

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This PR syncs the LevelDB subtree to import a refactor changing header `static const` variables to `inline constexpr`. The update resolves compiler warnings, directly unblocking PR #36275 to enable `-Wunused-const-variable`. The diff is small (+16/-16), passes CI, and has already received a code review ACK.