perf python: Add __str__ and __repr__ functions to evsel

perf python: Add __str__ and __repr__ functions to evsel

This allows evsel to be shown in the REPL like:

  Python 3.11.9 (main, Jun 19 2024, 00:38:48) [GCC 13.2.0] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  >>> import sys
  >>> sys.path.insert(0, '/tmp/perf/python')
  >>> import perf
  >>> x=perf.parse_events('cycles,data_read')
  >>> print(x)
  evlist([cycles,uncore_imc_free_running_0/data_read/,uncore_imc_free_running_1/data_read/])
  >>> x[0]
  evsel(cycles)
  >>> x[1]
  evsel(uncore_imc_free_running_0/data_read/)
  >>> x[2]
  evsel(uncore_imc_free_running_1/data_read/)

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Veronika Molnarova <vmolnaro@redhat.com>
Cc: Weilin Wang <weilin.wang@intel.com>
Link: https://lore.kernel.org/r/20241119011644.971342-22-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>