fix(jfr): parser fixes

[korniltsev]

The main fix is in frames function

Before the PR it was generating class + "." + function string every time the function was referenced in any stacktrace, now it is generated lazily once per function.

goos: linux
goarch: amd64
pkg: github.com/grafana/pyroscope/pkg/ingester/pyroscope
cpu: AMD Ryzen 9 5950X 16-Core Processor            
                                                                │   old.txt    │               new.txt               │
                                                                │    sec/op    │   sec/op     vs base                │
IngestJFR/cortex-dev-01__kafka-0__cpu_lock0_alloc0__0.jfr.gz-32   149.88m ± 2%   75.19m ± 3%  -49.83% (p=0.000 n=10)

                                                                │   old.txt    │               new.txt                │
                                                                │     B/op     │     B/op      vs base                │
IngestJFR/cortex-dev-01__kafka-0__cpu_lock0_alloc0__0.jfr.gz-32   46.59Mi ± 0%   29.31Mi ± 0%  -37.09% (p=0.000 n=10)

                                                                │   old.txt   │               new.txt               │
                                                                │  allocs/op  │  allocs/op   vs base                │
IngestJFR/cortex-dev-01__kafka-0__cpu_lock0_alloc0__0.jfr.gz-32   543.9k ± 0%   159.4k ± 0%  -70.70% (p=0.000 n=10)

[kolesnikovae]

LGTM