The tail call resolution logic was duplicated in `Environment::call` and
`VM::run`. This commit extracts the tail call resolution logic into a
single method `VM::resolve_tail_calls` and uses it in both places.
Additionally, this commit adds support for series indexing as a form of
tail call, allowing for direct access to series elements through the
`series(index)` syntax. This is useful for back-referencing in
time-series data.
A new example `err.myc` is added to demonstrate basic series usage and
error handling.
This commit introduces the BNF for the Myc language, along with its core
semantics, data types, and evaluation logic. It also details the macro
system and provides an overview of the standard library. This document
serves as a foundational context for LLMs to understand and generate Myc
code.