Bugs fixed (not covered by PR #40197):
- unittests.c: Fix get_addr_info test entry pointing to wrong handler
  (GetSetIdTestEntry -> GetAddrInfoTestEntry)
- SocketChannel.h: Fix %s format specifier in fmt-style LOG_ERROR on
  Linux; channel name was silently dropped from protocol error logs
- p9file.cpp: Fix readlinkat return type (int -> ssize_t) to match
  POSIX specification
- configfile.cpp: Guard ungetwc() call against WEOF to avoid undefined
  behavior on some implementations
- init.cpp: Fix SIGCHLD race by blocking the signal before setting the
  handler, preventing a window where child exit could be lost
- util.cpp: Extract duplicated signal skip list into SkipSignal() helper
  to ensure consistency between save and set handlers

Test improvements:
- NetworkTests.cpp: Add SO_RCVTIMEO timeout on accept() to prevent
  indefinite test hangs (resolves TODO)
- DrvFsTests.cpp: Add LOG_IF_WIN32_BOOL_FALSE to cleanup operations
  to surface silent file/directory deletion failures

Script hardening:
- copy_and_build_tests.ps1: Replace Invoke-Expression with call operator
  to prevent command injection via interpolated variables
- test-setup.ps1: Pass PostInstallCommand through bash -c for proper
  shell argument handling
- deploy-to-vm.ps1: Prompt for password via Read-Host -AsSecureString
  when not provided, instead of creating empty SecureString

Resource management:
- WslConfigService.cs: Dispose FileSystemWatcher in destructor to
  prevent resource leak

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Full deep review covering 7 subsystems with 44 findings.
12 fixes on this branch, 10+ already in PR #40197, 4 deferred.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sizeof(index) incorrectly resolved to a C library function type instead
of the Index parameter, causing a build error on Linux. Fix the casing
to match the parameter name.

Introduced in 58bd525 (#40197).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sizeof(index) incorrectly resolved to a C library function type instead
of the Index parameter, causing a build error on Linux. Fix the casing
to match the parameter name.

Introduced in 58bd525 (#40197).

Co-authored-by: Ben Hillis <benhill@ntdev.microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>