fix(parser): print the trace once in @def trace mode (#344)

[ocots]

Closes #344.

Sibling of #345 — both branch from chore/deps-examodels-0.12 and target it, so they can be reviewed and merged in any order (no overlap: this touches def_fun, #345 touches p_constraint!).

Problem

@def name … end true (trace mode) printed the parsed model twice, identical apart from gensym numbers.

When the :exa backend is active (the default), def_fun parses the definition once with backend=:fun and then, because is_active_backend(:exa), calls def_exa(e; log=log) to embed the ExaModels builder — a second parse! pass. Both passes run their log && println(...) traces.

Change

The :exa sub-parse inside def_fun now runs with log=false; the :fun pass already emitted the trace.

if is_active_backend(:exa)
    build_exa = def_exa(e; log=false)   # was: log=log
    ...

Public API

No change — only the duplicated trace output goes away.

Tests

test/test_onepass_fun.jl ("log" testset): captures stdout around CTParser.def_fun(ex; log=true) with :exa active and asserts each trace marker appears exactly once.

Full suite green locally: 2594 pass, 9 broken (pre-existing), 0 fail/error.

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