Fix infinite loop in LinuxPerfScriptEventParser on truncated sched_switch lines
Summary
Fixes an infinite loop (parser hang) in LinuxPerfScriptEventParser when parsing malformed or truncated sched_switch lines.
ReadProcessNameUntilNextField loops until it finds the expected next field name (e.g. prev_pid, next_pid, pid). If that field name never appears before the end of the stream — as happens with truncated/malformed perf script input — the loop never terminated and the parser hung indefinitely.
Root cause
The while (true) loop in ReadProcessNameUntilNextField had no end-of-stream termination condition. At EOF, FastStream returns a sentinel and ReadFixedString never matches the target field name, so the loop spins forever appending spaces.
Fix
Break out of the loop when source.EndOfStream is reached.
How it was found
OneFuzz fuzzing of the Linux perf script parser produced 146 hang inputs (out of 155 recorded crashes). All 146 replayed as 30s timeouts before this change; with the fix all inputs terminate cleanly.
Test
Adds LinuxPerfScriptEventParserTests.TruncatedSchedSwitchDoesNotHang, which parses a truncated sched_switch line and asserts parsing terminates (fails via timeout if the infinite loop regresses). Passes on net462 and net8.0.