Add Unique() filter method (#248)

Add Unique filter method to Pipe

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Co-authored-by: John Arundel <john@bitfieldconsulting.com>

Add Shell method for running commands via the system shell (#245)

* Add Shell method for running commands via the system shell

Adds ExecCommand(name, args...), which runs a command directly with
no parsing, holding the shared stdin/stdout/stderr/env/context/
error-handling logic.

Exec is now a thin wrapper that splits cmdLine with shell.Fields and
delegates to ExecCommand. A shell.Fields parse error is now surfaced
immediately via p.WithError, rather than only becoming visible once
the pipe is read; this is covered by
TestExec_SetsErrorImmediatelyOnInvalidCommandLineSyntax.

Shell runs cmdLine via the operating system's native shell (sh -c on
Unix-like systems, cmd /C on Windows, chosen via runtime.GOOS), by
calling ExecCommand directly with cmdLine as a single, completely
unmodified argument. This fixes the WithEnv/variable-expansion bug
described in #239, since the shell alone is responsible for parsing
and expansion, with no local re-interpretation of the command line.

Tested on both Linux and Windows.

* tweaks

* bump to go1.26.6 for GO-2026-6218, GO-2026-6090, GO-2026-5972, GO-2026-5856, GO-2026-5026

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Co-authored-by: Dhanalakshmi-D04 <dhanalakshmidgowda04@gmail.com>
Co-authored-by: John Arundel <john@bitfieldconsulting.com>

Lowered go.mod to 1.25.0 (#242)

* Lowered go.mod to 1.25.0

This restores support for consumers still using Go 1.25. The previous bump to `go 1.26.4` forced all consumers of this library to use Go 1.26 or newer.
The codebase does not use any Go 1.26-specific features, making the `1.26` language requirement unnecessary.

`go1.25.11` contains the same critical security patches as `go1.26.4` (fixing vulnerabilities in `crypto/x509`, `net/textproto`, and `mime`).
Go's toolchain auto-switching (introduced in Go 1.21) will automatically download and use `go1.25.11` for developers working on this module if their local toolchain is older, ensuring they build with the secure version without forcing a major Go upgrade.

* Changed toolchain to 1.26.4

This makes govulncheck work even for users with go1.26.{0-3}

bump to go1.26.4 for GO-2026-5037, GO-2026-5039 (#241)

update changelog

update readme (#219)

release v0.23

Update First(n int) to read no more data than necessary (#199)

First(N) now closes its output after it has read N lines, terminating the pipe 
without consuming unnecessary further input (apart from the 4KiB scanner 
buffer).

Co-authored-by: John Arundel <john@bitfieldconsulting.com>

Refactor

Filter: preserve previous error if func succeeds