perf: simplify export enumeration

[reubeno]

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[github-actions]

Test Results

    2 files      9 suites   1m 30s ⏱️
  663 tests   663 ✅ 0 💤 0 ❌
1 312 runs  1 312 ✅ 0 💤 0 ❌

Results for commit c7c581d.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	18.19 μs	18.13 μs	-0.06 μs	⚪ Unchanged
eval_arithmetic	0.17 μs	0.17 μs	-0.00 μs	⚪ Unchanged
expand_one_string	1.60 μs	1.60 μs	0.00 μs	⚪ Unchanged
for_loop	35.85 μs	34.38 μs	-1.46 μs	🟢 -4.09%
function_call	2.80 μs	2.79 μs	-0.01 μs	⚪ Unchanged
instantiate_shell	56.73 μs	57.76 μs	1.03 μs	🟠 +1.82%
instantiate_shell_with_init_scripts	21063.80 μs	22108.74 μs	1044.94 μs	🟠 +4.96%
parse_bash_completion	1649.74 μs	1644.08 μs	-5.66 μs	⚪ Unchanged
parse_sample_script	1.73 μs	1.73 μs	-0.01 μs	⚪ Unchanged
run_echo_builtin_command	15.78 μs	16.26 μs	0.48 μs	⚪ Unchanged
run_one_external_command	2350.22 μs	2334.11 μs	-16.11 μs	🟢 -0.69%
tokenize_sample_script	2.90 μs	2.88 μs	-0.02 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/arithmetic.rs	🟢 98.47%	🟢 98.48%	🟢 0.01%
brush-core/src/builtins/declare.rs	🟢 82.5%	🟢 83.15%	🟢 0.65%
brush-core/src/builtins/dot.rs	🟢 95.83%	🟢 95.45%	🔴 -0.38%
brush-core/src/builtins/getopts.rs	🟢 95.12%	🟢 95.06%	🔴 -0.06%
brush-core/src/builtins/set.rs	🟢 77.17%	🟢 76.82%	🔴 -0.35%
brush-core/src/env.rs	🟢 87.45%	🟢 88.42%	🟢 0.97%
brush-core/src/expansion.rs	🟢 96.23%	🟢 96.24%	🟢 0.01%
brush-core/src/interp.rs	🟢 91.47%	🟢 91.43%	🔴 -0.04%
brush-core/src/options.rs	🟢 90.38%	🟢 93.48%	🟢 3.1%
brush-core/src/shell.rs	🟢 78.73%	🟢 82.65%	🟢 3.92%
brush-core/src/sys/unix/terminal.rs	🔴 32.65%	🔴 38.78%	🟢 6.13%
brush-core/src/sys/unix/users.rs	🔴 28.95%	🔴 38.64%	🟢 9.69%
brush-core/src/variables.rs	🟢 82.3%	🟢 83.3%	🟢 1%
brush-interactive/src/interactive_shell.rs	🟠 74.68%	🟠 72.84%	🔴 -1.84%
Overall Coverage	🟢 75.2%	🟢 75.66%	🟢 0.46%

Minimum allowed coverage is 70%, this run produced 75.66%