Vec::append() => Vec::extend()

[atuchin-m]

For brave/brave-browser#50463

The PR optimizes the peak memory usage by 5%.
append() doesn't drop the capacity of vec, it just calls set_len(0)

[github-actions]

Rust Benchmark

Benchmark suite	Current: bb4a771	Previous: 013f82a	Ratio
rule-match-browserlike/brave-list	2347667449 ns/iter (± 20286775)	2415314808 ns/iter (± 32783519)	0.97
rule-match-first-request/brave-list	1115395 ns/iter (± 10519)	1136036 ns/iter (± 33574)	0.98
blocker_new/brave-list	187657044 ns/iter (± 1689084)	191587636 ns/iter (± 2413020)	0.98
blocker_new/brave-list-deserialize	27836768 ns/iter (± 904659)	30894729 ns/iter (± 761050)	0.90
memory-usage/brave-list-initial	10212224 ns/iter (± 3)	10212224 ns/iter (± 3)	1
memory-usage/brave-list-initial/max	64057431 ns/iter (± 3)	67489115 ns/iter (± 3)	0.95
memory-usage/brave-list-initial/alloc-count	1610823 ns/iter (± 3)	1610823 ns/iter (± 3)	1
memory-usage/brave-list-1000-requests	2666926 ns/iter (± 3)	2666926 ns/iter (± 3)	1
memory-usage/brave-list-1000-requests/alloc-count	71337 ns/iter (± 3)	71337 ns/iter (± 3)	1
url_cosmetic_resources/brave-list	198816 ns/iter (± 1282)	203591 ns/iter (± 1162)	0.98
cosmetic-class-id-match/brave-list	3353399 ns/iter (± 943854)	3406731 ns/iter (± 908867)	0.98

This comment was automatically generated by workflow using github-action-benchmark.