Add fxmacrodata module

[roberttidball]

This adds a small fxmacrodata module that wraps the FXMacroData REST API (economic indicator releases, release calendars and FX spot rates) and returns plain Nushell tables.

use modules/fxmacrodata

fxmacrodata catalogue usd                          # indicators available for a currency
fxmacrodata history usd inflation --limit 12       # release history, most recent first
fxmacrodata calendar usd --indicator inflation     # upcoming scheduled releases
fxmacrodata forex eur usd --limit 30               # daily FX rates (needs a key)

• Epoch and date fields are converted to datetime columns, so things like where release_time < ((date now) + 2wk) just work.
• USD works without a key. If $env.FXMACRODATA_API_KEY is set it is sent as an X-API-Key header (never in the URL).
• Free-tier notices from the API (90-day history window, 15 minute release delay) are printed to stderr so they don't end up in the table.
• Every command takes --raw to get the untouched JSON response.

Checked with nu-check --as-module on nu 0.116.1, and ran each command against the live API.

[roberttidball]

Small hardening pass: requests no longer follow redirects, so the API key is never re-sent to another host, the key is trimmed before use, and a 200 response with an error body or an unexpected shape now raises a clear error instead of a missing-column failure. (not run locally)

[fdncred]

Thanks