feat: ✨ add namespace prefix filtering to createEnvParser

[iamnewton]

Summary

• Adds namespaces?: string[] to EnvParserOptions
• When set, only env vars whose names start with one of those prefixes (case-insensitive, followed by _) are visible to the parser — the prefix is stripped before key normalisation
• Priority order: first namespace in the array wins when the same key appears under multiple prefixes
• New utilities filterByNamespace and mergeNamespaces are exported from the package root for direct use

Motivation

CLIs built from the cli-template each have their own namespace (e.g. CLI_TEMPLATE_). But you may also want a shared org-wide namespace (e.g. HOLOCRON_) set once in ~/.bashrc that any tool can fall back to without copying vars into every project's .env.

// CLI_TEMPLATE_DEBUG overrides HOLOCRON_DEBUG; HOLOCRON_VERBOSE is still visible
const parser = createEnvParser({
  appName: "my-cli",
  namespaces: ["CLI_TEMPLATE", "HOLOCRON"],
});
const debug = parser.get("debug");   // CLI_TEMPLATE_DEBUG ?? HOLOCRON_DEBUG
const verbose = parser.get("verbose"); // HOLOCRON_VERBOSE

Test plan

• pnpm --filter @theholocron/env-utils build — clean build
• pnpm --filter @theholocron/env-utils test — 138/138 tests pass (10 new in filter-by-namespace, 6 new in create-env-parser)
• CI lint, typecheck, test pass

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@            Coverage Diff             @@
##             main     #213      +/-   ##
==========================================
+ Coverage   97.30%   97.43%   +0.12%     
==========================================
  Files          21       22       +1     
  Lines         223      234      +11     
  Branches       55       57       +2     
==========================================
+ Hits          217      228      +11     
  Partials        6        6              

Files with missing lines	Coverage Δ
packages/env-utils/src/create-env-parser.ts	100.00% <100.00%> (ø)
...ackages/env-utils/src/utils/filter-by-namespace.ts	100.00% <100.00%> (ø)

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[iamnewton]

🎉 This PR is included in version 1.2.0 🎉

The release is available on:

• v1.2.0
• GitHub release

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