🩹 [Patch]: Add Test-Toml to validate TOML without throwing

[Marius Storhaug (MariusStorhaug)]

Adds Test-Toml, a pure-validator that returns [bool] — never throws — so scripts can safely probe TOML content before (or instead of) parsing it. The design mirrors PowerShell's built-in Test-Json.

New: Validate TOML content safely

Test-Toml wraps ConvertFrom-Toml in a try/catch. On success it returns $true; on any parser error it writes a non-terminating error to the error stream and returns $false.

# Validate a string
Test-Toml -InputObject 'key = "value"'    # $true
'[invalid' | Test-Toml                    # $false + error written

# Validate a file
Test-Toml -Path .\Cargo.toml              # $true if file is valid TOML
Test-Toml -LiteralPath 'C:\app\cfg.toml'  # literal path variant

Parameter sets

Parameter	Set	Notes
-InputObject	Default	Pipeline-capable; [AllowEmptyString()] so '' returns $false
-Path	Path	Resolves relative paths
-LiteralPath	LiteralPath	No wildcard expansion

Key implementation notes

• [AllowEmptyString()] is required on InputObject: PowerShell's mandatory parameter binding rejects '' without it, whereas the correct behaviour is $false.
• Write-Error is always called from inside a catch block with -ErrorAction Continue to ensure non-terminating behaviour even when $ErrorActionPreference = 'Stop' is set module-wide.
• No new parser logic — reuses ConvertFrom-Toml to keep validation consistent with parsing.

Technical Details

• File added: src/functions/public/Test-Toml.ps1
• Tests added: Describe 'Test-Toml' block in tests/Toml.Tests.ps1 (11 new tests; total 135, all passing)
• PSScriptAnalyzer: No new warnings introduced (pre-existing BOM and OutputType notices in other files unchanged)
• No alias: The issue mentions Test-Tml but aliases are not in the current module standards

Details

Closes #4