selfhost: fix parser infinite loop + lexer token limit

- Parser_Parse: add beforePos safeguard to skip unrecognized tokens
  instead of looping forever when parserParseDecl returns null
- Lexer: increase maxTokens 4096 -> 32768; add explicit break on limit
- CLI: null-check ReadFile result before String_Eq
- Nim CLI: add -O2 to cc invocation for faster self-hosted builds

src/cli.nim

@@ -536,7 +536,7 @@ proc cmdBuild*(args: seq[string], opts: GlobalOptions): int =
   # Compile with cc
   let outputName = if man.name != "": man.name else: "bux_out"
   let outputFile = buildDir / outputName
-  let ccCmd = &"cc -pthread -o {outputFile} {cFile} {runtimeDst} {ioDst} -lm 2>&1"
+  let ccCmd = &"cc -O2 -pthread -o {outputFile} {cFile} {runtimeDst} {ioDst} -lm 2>&1"
   if opts.verbose:
     printInfo(&"running: {ccCmd}", useColor)
   let (output, exitCode) = execCmdEx(ccCmd)