UPLC textual parser (plutus-core 1.45.0.0): fails to parse large (case (constr 0 ...) (lam ...)) when branch body is ~490 lines

## Summary

The megaparsec-based UPLC textual parser in `plutus-core 1.45.0.0` fails to parse a syntactically valid `(case (constr 0 b1..b8) (lam ...))` expression when the single case branch contains a body of approximately 490 lines. The error position reported is misleading (points to the outer `(lam` start) due to megaparsec backtracking.

## Reproduction

**File:** the HTLC scenario from [Unisay/scalus-cape-submissions](https://github.com/Unisay/scalus-cape-submissions), commit `0846510184d98b054c4405c4d036154444467d9f`, file `src/htlc/htlc.uplc`.

- Size: 51 700 bytes
- SHA-256: `abd5609f2da11b37cdb71d8314b34d94012bee1f3b2a3b43793a715228818493`
- Program header: `(program 1.1.0 ...)`

**Trigger structure** (outer program body, lines 1–5 of the file):

```uplc
(program 1.1.0 (case (constr 0
(force (force (builtin chooseList)))
(force (force (builtin fstPair))) (force (builtin headList))
(force (builtin ifThenElse)) (force (builtin mkCons))
(force (force (builtin sndPair))) (force (builtin tailList))
(force (builtin trace))) (lam __builtin_ChooseList
(lam __builtin_FstPair
...~490 lines of body...
))))
```

**How to reproduce:**

```haskell
import UntypedPlutusCore.Parser (parseProgram)
import Data.Text.IO qualified as T

main :: IO ()
main = do
src <- T.readFile "htlc.uplc"
case parseProgram src of
Left err -> print err
Right _ -> putStrLn "OK"
```

**Error:**

```
test:5:32:
5 | (force (builtin trace))) (lam __builtin_ChooseList
| ^
unexpected '('
expecting ')'
```

## What was ruled out

- **Paren balance:** 437 opens = 437 closes. File is well-formed.
- **`case`/`constr` support:** parser version 1.45.0.0 does support `case`/`constr` (language version 1.1.0). fibonacci Scalus 0.16.0 UPLC in the same repo — which also uses `(force (case (constr 0 ...) ...))` but with a small body — **parses and verifies fine**.
- **Constants:** removing `(con string …)` and `(con data …)` constants does not change the failure.
- **Structure in isolation:** a minimal `(case (constr 0 b1..b8) (lam x1 (lam x2 ... (lam x8 small-body))))` parses fine.
- **Hidden characters / encoding:** no BOM, no CRLF, plain UTF-8.

## Root cause hypothesis

`caseTerm` in `UntypedPlutusCore/Parser.hs` uses `many term` for branches. When `term` starts parsing the `(lam __builtin_ChooseList ...)` branch and then fails somewhere deep inside the ~490-line body, megaparsec's `many` backtracking causes the error to be reported at the outermost `(` of the failed branch (line 5:32) rather than at the actual failure site. The actual parser error is lost and the reported position is misleading.

The underlying issue may be one of:
1. A missing `try` combinator on one of the sub-parsers inside `term`, causing megaparsec to incorrectly drop progress and backtrack to the `many term` boundary.
2. An error inside the branch body that is not recoverable — the parser cannot finish parsing `(lam __builtin_ChooseList BODY)` due to some construct inside BODY — but the reported location is wrong.

## Impact

Any UPLC file generated by Scalus 0.16.0's `toUplcOptimized()` for contracts with 8+ forced builtins (e.g. HTLC, other Cardano V3 validators) will fail to parse under `plutus-core ^>=1.45`. The workaround is to use `toUplc()` (no CaseConstrApply optimization), which produces larger but parseable UPLC.

This blocks UPLC-CAPE benchmark submissions for complex Scalus 0.16.0 contracts.

## Environment

- `plutus-core`: 1.45.0.0
- Parser: `UntypedPlutusCore.Parser.parseProgram` (megaparsec-based)
- UPLC language version: `1.1.0` (Plutus V3 / Conway)
- Confirmed via `cabal repl` in UPLC-CAPE repo