fix: don't fail importing unreadable history lines

[reubeno]

There's more that we should do to ensure history importing isn't fatal, but this change at least ensures that history lines with bytes not parseable as UTF-8 won't cause brush to fail outright.

Also adds a test case that reproduced the reported issues and confirms that it's fixed now.

Resolves #702

[github-actions]

Test Results

    3 files     23 suites   6m 12s ⏱️
  877 tests   877 ✅ 0 💤 0 ❌
2 611 runs  2 611 ✅ 0 💤 0 ❌

Results for commit 75fdf1b.

♻️ This comment has been updated with latest results.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	17.70 μs	17.58 μs	-0.12 μs	🟢 -0.66%
eval_arithmetic	0.15 μs	0.15 μs	-0.00 μs	⚪ Unchanged
expand_one_string	1.95 μs	1.91 μs	-0.04 μs	⚪ Unchanged
for_loop	22.43 μs	22.30 μs	-0.12 μs	⚪ Unchanged
function_call	2.42 μs	2.54 μs	0.11 μs	🟠 +4.75%
instantiate_shell	58.62 μs	58.13 μs	-0.49 μs	🟢 -0.84%
instantiate_shell_with_init_scripts	22389.82 μs	22407.98 μs	18.16 μs	⚪ Unchanged
parse_bash_completion	1664.25 μs	1684.87 μs	20.63 μs	⚪ Unchanged
parse_sample_script	1.77 μs	1.78 μs	0.01 μs	⚪ Unchanged
run_echo_builtin_command	15.92 μs	15.71 μs	-0.21 μs	⚪ Unchanged
run_one_external_command	2363.34 μs	2855.34 μs	492.00 μs	🟠 +20.82%
tokenize_sample_script	2.75 μs	2.75 μs	-0.00 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/history.rs	🟠 68.1%	🟠 68.69%	🟢 0.59%
Overall Coverage	🟢 72.48%	🟢 72.49%	🟢 0.01%

Minimum allowed coverage is 70%, this run produced 72.49%

Test Summary: bash-completion test suite

Outcome	Count	Percentage
✅ Pass	1305	61.88
❗️ Error	233	11.05
❌ Fail	184	8.72
⏩ Skip	372	17.64
❎ Expected Fail	15	0.71
📊 Total	2109	100.00