[sairex53]

memleak currently builds allocator probe names by prepending --symbols-prefix to standard names. That does not cover allocators such as jemalloc 5.3, where the relevant entry points can be je_malloc_default and je_free_default.

Add --malloc-symbol and --free-symbol to both Python and libbpf memleak. The exact names override the corresponding prefixed defaults. Add regression coverage for allocations and frees through custom symbols, and document the options.

Fixes #5392.

Testing:

• make -C libbpf-tools memleak — passed
• Python syntax checks, test fixture compilation, CLI parsing, and git diff --check — passed
• BPF integration tests could not run locally because pyroute2 is missing and the session has no effective BPF privileges.