Bump nanobruijn to e6e112a (OSNF)

[nomeata]

Summary

• Bump nanobruijn to e6e112a which adds OSNF (Outermost-Shift Normal Form) parse-time normalization
• Expressions with fvar_lb > 0 are stored as Shift(fvar_lb, core) where core has fvar_lb = 0
• Shift-equivalent expressions share cores in the DAG, improving TC cache hit rates across binder depths
• A/B/A test on full Mathlib: -7% user time (1175s → 1095s), +18% RSS (7.9GB → 9.3GB)

Test plan

• Passes Init (54K declarations)
• Passes full Mathlib (630K declarations, 0 errors)
• Arena CI

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