roi: more input sanity checks (fixes #2505)

[adept]

This checks for:

• catch-all queries supplied to --pnl, which will cause no transactions to be classed as "investment" (root cause of hledger roi --inv "^assets:investments" --pnl "" errors #2505)

• mixed commodities in cashflow / pnl transactions, as we can't add apples to oranges to compute a sensible rate of return

At the moment both of these cases fail with undecipherable error from the bowels of IRR computation. Let's fail with a sensible error message instead, and provide a path to resolution, if possible

[simonmichael]

This looks like a great error message improvement. Does it really fix #2505 as the message states ? That was the following not-so-clear message:

> stack run hledger -- roi --file="/tmp/roi.journal" --value="then,€" --inv "^assets:.*:TICK$" --pnl ""
hledger: Error: Error (NotBracketed): No solution for Internal Rate of Return (IRR).

[adept]

Yep, with --pnl "" (which is parsed as Any) you get:

hledger: Error: Need some transactions classed as investment and not pnl, but the pnl query matches any transaction - will be unable to compute the rates of return

[adept]

And if you fix that and instead, say, omit` --value, you get:

> stack run hledger -- roi --file="/tmp/roi.journal" --inv "^assets:.*:TICK$" --pnl "__none__"
hledger: Error: Period (2025-08-14,2025-10-24) has multiple commodities: TICK, €
Consider using --value to force all costs to be in a single commodity.
For example, "--value=end,<commodity> --infer-market-prices", where commodity is the one that you want to value the investment in.

[simonmichael]

The #2505 error message is still present in the code though.

It has more helpful additional text than I noticed before. Perhaps we can just remove the "Error (NotBracketed): " prefix there, as Error is is already printed by hledger and NotBracketed isn't needed by users (likewise for the line below).