Implement CRuby-compatible command-line option processing

[sisshiki1969]

Summary

Running ruby/spec's command_line category against monoruby (with CRuby 4.0.2 as the reference) showed 146 failures + 1 error out of 175 examples, almost all rooted in the clap-based CLI rejecting CRuby's switches with exit status 2. This PR replaces the CLI with a hand-rolled CRuby-style option parser, wires up the semantics the specs exercise, aligns the uncaught-error report with CRuby, and implements chilled string literals.

Result: 175 examples, 0 failures (command_line category, release build).

Changes

Option parser (main.rs)

• Clustered short switches with attached values (-naF:, -072, -Ke, -ne '...'), -- terminator, CRuby-style invalid option errors (exit 1).
• -v / --version / --copyright print RUBY_DESCRIPTION / RUBY_COPYRIGHT; -v alone exits without reading stdin.
• -w / -W[level] / -W:category wired to $VERBOSE and Warning[]; -d/--debug sets $DEBUG and $VERBOSE.
• -c syntax check, -s switch-to-global parsing, -C/-X chdir, -x[dir] shebang scan (plus the automatic scan when the first line is a non-ruby #!), -S RUBYPATH/PATH lookup.
• RUBYOPT processing with CRuby's allowed-switch subset (invalid switch in RUBYOPT otherwise); RUBYLIB prepended to $LOAD_PATH; -I now prepends with File.expand_path semantics (no symlink resolution).
• --enable/--disable features: gems, did_you_mean, rubyopt, frozen-string-literal, all (unknown features warn); --disable-gems keeps working via the generic feature path.
• -E/-U/-K/--encoding/--external-encoding/--internal-encoding set the default external/internal encodings; -U vs -E ext:int conflict rejected like CRuby.

-n / -p loop (parser/)

The implicit while gets ... end wrap is synthesized at the AST level in the prism lowerer (armed per main-script path, consumed on first match), so BEGIN/END blocks still hoist and run exactly once. -a adds $F = $_.split, -l adds $_ = $_.chomp($/) and $\ = $/, -p appends print $_.

Error report alignment + --backtrace-limit

• Uncaught runtime errors now print CRuby's compact report (file:line:in 'meth': msg (Class) + TAB-indented from frames); the source excerpt with a caret is kept for SyntaxError only, matching CRuby.
• --backtrace-limit=N truncates frames to N plus ... K levels..., both in the top-level report and in Exception#full_message (which now uses detailed_message, i.e. msg (Class)).
• The toplevel frame displays as <main> (CRuby) instead of the internal /main name.

Chilled string literals (CRuby 3.4 migration path)

• String literals in pragma-less files are chilled: first mutation warns literal string will be frozen in the future ... (gated by Warning[:deprecated]). The template is flag-marked at bytecode emission; Value::value_deep_copy propagates the mark, covering the VM and both JIT backends through the single shared runtime hook.
• --debug / --debug-frozen-string-literal records literal creation sites: FrozenError gains , created at file:line; the chilled warning is followed by file:line: warning: the string was created here.
• String#+@ is now a Rust builtin that dups frozen and chilled receivers, so the +"literal" idiom mutates silently, like CRuby.
• monoruby's own runtime Ruby (builtins / stdlib stubs under the install root) is exempt from chilling — CRuby's stdlib counterparts all carry explicit pragmas.

Runtime support

• Kernel#gets honours $/ (nil = slurp, "" = paragraph mode) and reads ARGV files ARGF-style before falling back to stdin.
• IO#puts stringifies non-String values through their to_s method.
• $-a / $-l / $-p gvar mirrors reflect the actual CLI switches (still read-only).
• Encoding.find resolves filesystem / locale / external / internal.
• The hyphenated # frozen-string-literal: magic-comment spelling (used by the stock rbconfig.rb) is now recognized.

Testing

• ruby/spec command_line: 146 failures + 1 error → 0 failures (release build, CRuby 4.0.2 reference).
• ruby/spec core/string + core/set: 171 → 168 failures (3 fixed by chilled literals), no new errors.
• cargo test --lib --tests: all 30 suites green locally.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XpzdoFu46d2ChJpSzeWsNK

[codecov]

Codecov Report

❌ Patch coverage is 86.79078% with 149 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.87%. Comparing base (f6b232e) to head (686cace).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
monoruby/src/main.rs	88.87%	68 Missing ⚠️
monoruby/src/builtins/kernel.rs	67.40%	44 Missing ⚠️
monoruby/src/value.rs	68.53%	28 Missing ⚠️
monoruby/src/builtins/encoding.rs	77.77%	4 Missing ⚠️
monoruby/src/builtins/io.rs	80.00%	1 Missing ⚠️
monoruby/src/bytecodegen.rs	97.50%	1 Missing ⚠️
monoruby/src/globals.rs	97.72%	1 Missing ⚠️
monoruby/src/globals/error.rs	97.22%	1 Missing ⚠️
monoruby/src/globals/gvar.rs	92.30%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #891      +/-   ##
==========================================
- Coverage   90.90%   90.87%   -0.04%     
==========================================
  Files         189      189              
  Lines      121624   122778    +1154     
==========================================
+ Hits       110563   111572    +1009     
- Misses      11061    11206     +145     

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