[cli] Make all short names upper cases + Enable pipe mode and file mode

[forfudan]

This PR updates the Decimo CLI to avoid short-flag collisions with negative expressions by uppercasing short options, and adds new stdin (pipe) + file-based input modes for evaluating multiple expressions.

Changes:

• Uppercase short flags for formatting/computation options (-P/-S/-E/-D/-R) and remove the --pad short flag to prevent collisions with expressions like -e, -pi, -sin(1).
• Add pipe mode (read/evaluate expressions from stdin, one per non-empty non-comment line) and file mode (-F/--file).
• Extend integration/unit tests and update docs/changelog/plans for the new CLI UX.

[Copilot]

Pull request overview

Updates the Decimo CLI to avoid short-flag collisions with negative expressions by uppercasing short options, and adds new input modes for evaluating expressions from stdin (pipe) and from a file.

Changes:

• Uppercase all short option names (-P/-S/-E/-D/-R) and remove the --pad short flag to prevent collisions with expressions like -e, -pi, -sin(1).
• Add pipe mode (read/evaluate expressions from stdin, one per line) and file mode (evaluate expressions from a -F/--file path).
• Extend integration + unit tests and update CLI documentation/changelog to reflect the new UX.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/test_cli.sh	Updates short flags and adds integration coverage for pipe mode and -F/--file mode.
tests/cli/test_io.mojo	Adds unit tests for new I/O helpers (line splitting, comment stripping, etc.).
src/cli/main.mojo	Implements mode detection (expr vs pipe vs file), new -F/--file option, and updated short flags.
src/cli/calculator/io.mojo	Introduces stdin/file reading and line-processing utilities used by pipe/file modes.
src/cli/calculator/init.mojo	Re-exports new I/O utilities from the calculator package.
docs/user_manual_cli.md	Documents new short flags and adds an “Input Modes” section.
docs/plans/cli_calculator.md	Updates CLI plan/status to mark pipe/file input and uppercase short flags as implemented.
docs/changelog.md	Notes pipe mode + file mode additions under “Unreleased”.

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[Copilot]

Pull request overview

This PR updates the Decimo CLI to avoid short-flag collisions with negative expressions by uppercasing short options, and adds new stdin (pipe) + file-based input modes for evaluating multiple expressions.

Changes:

• Uppercase short flags for formatting/computation options (-P/-S/-E/-D/-R) and remove the --pad short flag to prevent collisions with expressions like -e, -pi, -sin(1).
• Add pipe mode (read/evaluate expressions from stdin, one per non-empty non-comment line) and file mode (-F/--file).
• Extend integration/unit tests and update docs/changelog/plans for the new CLI UX.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/test_cli.sh	Updates integration tests for new short flags; adds pipe/file mode integration coverage.
tests/cli/test_io.mojo	Adds unit tests for new I/O helpers (splitting, comment stripping, etc.).
src/cli/main.mojo	Implements new input mode detection and pipe/file execution paths; updates CLI flags and help tips.
src/cli/calculator/io.mojo	Introduces stdin/file reading helpers and line filtering utilities for pipe/file mode.
src/cli/calculator/init.mojo	Re-exports the new calculator I/O utilities.
docs/user_manual_cli.md	Updates option reference and documents the three input modes + new flag casing.
docs/plans/cli_calculator.md	Updates plan/status notes to reflect completed pipe/file mode and new short flags.
docs/changelog.md	Adds unreleased changelog entries describing pipe/file mode additions.

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