fix(break,continue): use default_value_t for flag values

[Elsie19]

default_value is for types that can be converted into a String, which can be expensive, but default_value_t is for stack-allocated types and should be a less expensive to use.

At the level that you use default_value, it won't get us that much more performance, but it's still worth it.

#490 does the ones for mapfile.

[reubeno]

Nice! Righteous change.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	17.91 μs	18.26 μs	0.34 μs	🟠 +1.93%
eval_arithmetic	0.17 μs	0.17 μs	0.00 μs	⚪ Unchanged
expand_one_string	1.99 μs	1.82 μs	-0.17 μs	🟢 -8.48%
for_loop	23.60 μs	22.62 μs	-0.98 μs	🟢 -4.15%
function_call	2.95 μs	2.48 μs	-0.47 μs	🟢 -15.92%
instantiate_shell	57.71 μs	58.83 μs	1.12 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	26041.43 μs	24501.94 μs	-1539.49 μs	🟢 -5.91%
parse_bash_completion	1713.17 μs	1663.81 μs	-49.36 μs	🟢 -2.88%
parse_sample_script	1.73 μs	1.74 μs	0.01 μs	⚪ Unchanged
run_echo_builtin_command	15.65 μs	15.76 μs	0.10 μs	⚪ Unchanged
run_one_external_command	2114.40 μs	2357.40 μs	243.00 μs	🟠 +11.49%
tokenize_sample_script	2.92 μs	2.84 μs	-0.08 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/builtins/break_.rs	🟢 84.62%	🟢 85.71%	🟢 1.09%
brush-core/src/builtins/continue_.rs	🟢 93.33%	🟢 93.75%	🟢 0.42%
brush-core/src/jobs.rs	🔴 43.1%	🔴 37.07%	🔴 -6.03%
Overall Coverage	🟢 76.88%	🟢 76.81%	🔴 -0.07%

Minimum allowed coverage is 70%, this run produced 76.81%

Test Summary: bash-completion test suite

Outcome	Count	Percentage
✅ Pass	1300	61.64
❗️ Error	230	10.91
❌ Fail	196	9.29
⏩ Skip	368	17.45
❎ Expected Fail	14	0.66
✔️ Unexpected Pass	1	0.05
📊 Total	2109	100.00