[cli] Add configuration system for REPL to set all items per line

[forfudan]

This PR adds a REPL configuration system so users can change calculator display/computation options via :... meta-commands or inline expr:... one-off overrides.

Changes:

• Introduce Settings, parse_settings, and split_inline_settings for REPL configuration parsing.
• Integrate settings/meta-commands + inline overrides into the REPL loop; add extensive unit tests for the settings parser.
• Expand docstrings across CLI calculator modules and update planning/docs; adjust CLI delimiter flag (removes -D).

[Copilot]

Pull request overview

Adds a REPL configuration system so users can change calculator display/computation options via :... meta-commands or inline expr:... one-off overrides.

Changes:

• Introduce Settings, parse_settings, and split_inline_settings for REPL configuration parsing.
• Integrate settings/meta-commands + inline overrides into the REPL loop; add extensive unit tests for the settings parser.
• Expand docstrings across CLI calculator modules and update planning/docs; adjust CLI delimiter flag (removes -D).

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
tests/decimal128/test_decimal128_from_int.mojo	Fixes Decimal128.from_int(..., scale) calls to pass UInt32 scales.
tests/cli/test_settings.mojo	Adds thorough tests for settings parsing and inline settings splitting.
src/cli/main.mojo	Removes the -D short flag for --delimiter.
src/cli/calculator/tokenizer.mojo	Adds docstrings for token kinds and tokenizer helpers.
src/cli/calculator/settings.mojo	New settings model + parser and inline-settings splitter.
src/cli/calculator/repl.mojo	REPL now supports : meta-commands and inline expr:settings overrides via Settings.
src/cli/calculator/parser.mojo	Docstring improvements (args/returns).
src/cli/calculator/io.mojo	Docstring improvements (args/returns/examples).
src/cli/calculator/evaluator.mojo	Docstring improvements (args/returns).
src/cli/calculator/engine.mojo	Docstring improvements (args/returns).
src/cli/calculator/display.mojo	Docstring improvements and more documented ANSI constants.
src/cli/calculator/init.mojo	Re-exports the new settings API.
pixi.toml	Extends doc-generation task to include CLI calculator modules.
docs/plans/line_editor.md	Adds a detailed future plan for a Mojo line editor package.
docs/plans/cli_calculator.md	Updates roadmap/status notes for REPL features and CLI flag naming.

Comments suppressed due to low confidence (1)

src/cli/main.mojo:81

• Removing the delimiter short option (-D) is a breaking CLI change and will cause existing CLI integration tests and docs to fail (e.g. tests/test_cli.sh and docs/user_manual_cli.md still use -D). Either restore the short flag or update the tests/docs (and any completion/help output expectations) to match the new interface.

    var delimiter: Option[
        String,
        long="delimiter",
        help="Digit-group separator inserted every 3 digits (e.g. '_' gives 1_234.567_89)",
        default="",
        value_name="CHAR",
        group="Formatting",
    ]

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