fix(bdc): a company the filer tags as a member is not stripped as a prefix (#1373)

[mmitc]

Fixes #1373.

On <Company> | <Industry> | <Instrument> identifiers, a filer that also tags the company as a member puts its label among the member candidates. _match_company_candidate's prefix loop then stripped it as a grouping, stripped the industry, and returned the residue before the instrument cut: First Lien, Ordinary Shares, 9.1%. The same parse with no candidates named the company. from_xbrl passes the filing's candidates, so company_name carried the instrument.

Fix. In the prefix loop, a candidate that fills the whole first pipe segment is returned as the company. The check stays out of the way when that segment holds an instrument or a portfolio category (_known_investment_type_matches, _PORTFOLIO_CATEGORY_RE), because SLRC tags its headings (Senior Secured Loans, Common Equity/Equity Interests/Warrants) as members too. On SLRC's latest 10-Q that exception applies to 85 identifiers, all heading-led, which #1374 handles.

Measured over the latest 10-Q/10-K schedule of 42 BDCs (18,949 identifiers). Each was parsed with its own filing's member candidates, as from_xbrl does, before and after. 401 names move, every one from an instrument to the company. No investment_type moves, and the other 34 filers are unchanged:

filer	accession	moves	before → after (example)
CSWC	0000017313-26-000095	155 of 578	First Lien → AAC New Holdco Inc.
PSEC	0001287032-26-000269	142 of 248	First Lien → Abacus Dermatology Management, LLC
TPVG	0001580345-26-000025	58 of 311	Preferred Stock → Ao1 Holdings, Inc.
ARCC	0001628280-26-050307	24 of 1,478	Series G → Aerin Medical Inc.
BBDC	0001379785-26-000030	14 of 705	9.1% → Jocassee Partners LLC
OCSL	0001414932-26-000017	4 of 532	First Lien → Thrasio, LLC
NMFC	0001496099-26-000029	3 of 493	Class B-1 → TVG-Edmentum Holdings, LLC
OTF	0001747777-26-000028	1 of 497	Series D → HARNESS INC.

Every moved name equals the identifier's first pipe segment, with a trailing comma dropped in three ARCC rows (Vamos Bidco, Inc., → Vamos Bidco, Inc.).

Tests. tests/issues/regression/test_issue_1373.py, offline, covers the four identifiers from the issue, each with its own company as the one candidate, plus the issue's from_xbrl repro on a stub XBRL. tests/bdc and tests/issues/regression (not slow or network) show the same 13 failures on main in this Windows environment: filing-text baselines, legacy-parser lookups and #1325's import-ordering test. There are no new failures.

Composes with #1374 (the fix for #1372): merged together, the 42-filer run moves exactly the union of the two.

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